title stringlengths 12 150 | question_id int64 469 40.1M | question_score int64 2 5.52k | question_date stringdate 2008-08-02 15:11:16 2016-10-18 06:16:31 | answer_id int64 536 40.1M | answer_score int64 7 8.38k | answer_date stringdate 2008-08-02 18:49:07 2016-10-18 06:19:33 | tags listlengths 1 5 | question_body_md stringlengths 15 30.2k | answer_body_md stringlengths 11 27.8k |
|---|---|---|---|---|---|---|---|---|---|
Casting an int to a string in Python | 3,944,876 | 25 | 2010-10-15T18:08:49Z | 3,944,897 | 57 | 2010-10-15T18:10:59Z | [
"python",
"string",
"integer",
"concatenation"
] | I want to be able to generate a number of text files with the names fileX.txt where X is some integer:
```
for i in range(key):
filename = "ME" + i + ".txt" //Error here! Can't concat a string and int
filenum = filename
filenum = open(filename , 'w')
```
Does anyone else know how to do the filename = "ME"... | ```
x = 1
y = "foo" + str(x)
```
Please read the Python documentation: <http://docs.python.org/> |
Why is executemany slow in Python MySQLdb? | 3,945,642 | 12 | 2010-10-15T19:55:27Z | 3,945,860 | 18 | 2010-10-15T20:25:58Z | [
"python",
"sql",
"mysql",
"performance"
] | I am developing a program in Python that accesses a MySQL database using MySQLdb. In certain situations, I have to run an INSERT or REPLACE command on many rows. I am currently doing it like this:
```
db.execute("REPLACE INTO " + table + " (" + ",".join(cols) + ") VALUES" +
",".join(["(" + ",".join(["%s"] * len(co... | Try lowercasing the word 'values' in your query - this appears to be a bug/regression in MySQL-python 1.2.3.
MySQL-python's implementation of executemany() matches the VALUES clause with a regular expression and then just clones the list of values for each row of data, so you end up executing exactly the same query as... |
Find a specific tag with BeautifulSoup | 3,945,750 | 7 | 2010-10-15T20:11:02Z | 3,945,764 | 14 | 2010-10-15T20:13:04Z | [
"python",
"beautifulsoup"
] | I can traverse generic tags easily with BS, but I don't know how to find specific tags. For example, how can I find all occurances of `<div style="width=300px;">`? Is this possible with BS? | The following should work
```
soup = BeautifulSoup(htmlstring)
soup.findAll('div', style="width=300px;")
```
There are couple of ways to search for tags.
* <http://www.crummy.com/software/BeautifulSoup/documentation.html>
For more text to understand and use it
* <http://lxml.de/elementsoup.html> |
Converting string to tuple and adding to tuple | 3,945,856 | 4 | 2010-10-15T20:25:13Z | 3,945,883 | 9 | 2010-10-15T20:29:12Z | [
"python",
"string",
"tuples"
] | I have a config file like this.
```
[rects]
rect1=(2,2,10,10)
rect2=(12,8,2,10)
```
I need to loop through the values and convert them to tuples.
I then need to make a tuple of the tuples like
```
((2,2,10,10), (12,8,2,10))
``` | To turn the strings into tuples of ints (which is, I assume, what you want), you can use a regex like this:
```
x = "(1,2,3)"
t = tuple(int(v) for v in re.findall("[0-9]+", x))
```
And you can use, say, [configparser](http://docs.python.org/library/configparser.html) to parse the config file. |
Converting string to tuple and adding to tuple | 3,945,856 | 4 | 2010-10-15T20:25:13Z | 3,946,174 | 10 | 2010-10-15T21:11:54Z | [
"python",
"string",
"tuples"
] | I have a config file like this.
```
[rects]
rect1=(2,2,10,10)
rect2=(12,8,2,10)
```
I need to loop through the values and convert them to tuples.
I then need to make a tuple of the tuples like
```
((2,2,10,10), (12,8,2,10))
``` | Instead of using a regex or int/string functions, you could also use the `ast` module's `literal_eval` function, which only evaluates strings that are valid Python literals. This function is safe (according to the docs).
<http://docs.python.org/library/ast.html#ast.literal_eval>
```
import ast
ast.literal_eval("(1,2,3... |
Passing self into a constructor in python | 3,945,924 | 6 | 2010-10-15T20:35:01Z | 3,945,938 | 11 | 2010-10-15T20:36:46Z | [
"python",
"this",
"self"
] | I recently was working on a little python project and came to a situation where I wanted to pass `self` into the constructor of another object. I'm not sure why, but I had to look up whether this was legal in python. I've done this many times in C++ and Java but I don't remember ever having to do this with python.
Is ... | Yes it is legal, and yes it is pythonic.
I find myself using this pattern when you have an object and a container object where the contained objects need to know about their parent. |
What to consider before subclassing list? | 3,945,940 | 12 | 2010-10-15T20:37:00Z | 3,945,953 | 8 | 2010-10-15T20:39:26Z | [
"python",
"list",
"subclassing"
] | I was recently going over a coding problem I was having and someone looking at the code said that subclassing list was bad (my problem was unrelated to that class). He said that you shouldn't do it and that it came with a bunch of bad side effects. Is this true?
I'm asking if list is generally bad to subclass and if s... | I think the first question I'd ask myself is, "Is my new object really a list?". Does it walk like a list, talk like a list? Or is is something else?
If it is a list, then all the standard list methods should all make sense.
If the standard list methods don't make sense, then your object should contain a list, not be... |
What to consider before subclassing list? | 3,945,940 | 12 | 2010-10-15T20:37:00Z | 3,946,067 | 12 | 2010-10-15T20:57:04Z | [
"python",
"list",
"subclassing"
] | I was recently going over a coding problem I was having and someone looking at the code said that subclassing list was bad (my problem was unrelated to that class). He said that you shouldn't do it and that it came with a bunch of bad side effects. Is this true?
I'm asking if list is generally bad to subclass and if s... | The [abstract base classes](http://docs.python.org/glossary.html#term-abstract-base-class) provided in the [`collections`](http://docs.python.org/library/collections.html#abcs-abstract-base-classes) module, particularly `MutableSequence`, can be useful when implementing list-like classes. These are available in Python ... |
What to consider before subclassing list? | 3,945,940 | 12 | 2010-10-15T20:37:00Z | 3,946,763 | 14 | 2010-10-15T23:02:18Z | [
"python",
"list",
"subclassing"
] | I was recently going over a coding problem I was having and someone looking at the code said that subclassing list was bad (my problem was unrelated to that class). He said that you shouldn't do it and that it came with a bunch of bad side effects. Is this true?
I'm asking if list is generally bad to subclass and if s... | **There are no benefits to subclassing `list`.** None of the methods will use any methods you override, so you can have unexpected bugs. Further, it's very often confusing doing things like `self.append` instead of `self.foos.append` or especially `self[4]` rather than `self.foos[4]` to access your data. You can make s... |
How do I update an instance of a Django Model with request.POST if POST is a nested array? | 3,946,036 | 4 | 2010-10-15T20:51:43Z | 3,946,186 | 17 | 2010-10-15T21:12:39Z | [
"python",
"django",
"post",
"django-models",
"request"
] | I have a form that submits the following data:
```
question[priority] = "3"
question[effort] = "5"
question[question] = "A question"
```
That data is submitted to the URL /questions/1/save where `1` is the `question.id`. What I'd love to do is get question #1 and update it based on the POST data. I've got some of it ... | You can use a [ModelForm](http://docs.djangoproject.com/en/dev/topics/forms/modelforms/) to accomplish this. First define the ModelForm:
```
from django import forms
class QuestionForm(forms.ModelForm):
class Meta:
model = Question
```
Then, in your view:
```
question = Question.objects.get(pk=id)
if re... |
Python equivalent to Java's BitSet | 3,946,086 | 16 | 2010-10-15T20:59:46Z | 3,946,103 | 12 | 2010-10-15T21:02:45Z | [
"java",
"python",
"bitset"
] | Is there a Python class or module that implements a structure that is similar to the BitSet? | There's nothing in the standard library. Try:
<http://pypi.python.org/pypi/bitarray> |
Migrating from Stata to Python | 3,946,219 | 9 | 2010-10-15T21:16:45Z | 3,946,774 | 7 | 2010-10-15T23:05:33Z | [
"python",
"statistics",
"numpy",
"stata"
] | Some coworkers who have been struggling with Stata 11 are asking for my help to try to automate their laborious work. They mainly use 3 commands in Stata:
> tsset (sets a time series analysis)
as in: `tsset year_column, yearly`
> varsoc (Obtain lag-order selection statistics for VARs)
as in: `varsoc column_a column... | I believe both [scikits.timeseries](http://pytseries.sourceforge.net/) and [econpy / pytrix](http://code.google.com/p/econpy/) implement vector autoregression methods, but I haven't put either through their paces. |
Randomise order of if-else execution in Python | 3,946,488 | 3 | 2010-10-15T22:04:29Z | 3,946,512 | 11 | 2010-10-15T22:10:45Z | [
"python",
"random"
] | This might sound like a strange question, but bear with me...
I have a dictionary in Python with values like so:
```
'B': 23.6
'D': 0.6
'F': 35.9
'H': 35.9
```
I need to do an if-else with these values to do different things depending which one is > 30. The code I have at the moment is along the lines of:
```
if an... | You can make a sequence of key/value pairs:
```
pairs = angles.iteritems()
```
Filter it to remove elements <= 30:
```
filtered = [(name, value) for name, value in pairs if value > 30]
```
check to see if there are any options
```
if filtered:
```
and then pick one:
```
from random import choice
name, va... |
Does python urllib2 automatically uncompress gzip data fetched from webpage? | 3,947,120 | 56 | 2010-10-16T00:45:48Z | 3,947,241 | 123 | 2010-10-16T01:21:48Z | [
"python",
"gzip",
"urllib2"
] | I'm using
```
data=urllib2.urlopen(url).read()
```
I want to know:
1. How can I tell if the data at a URL is gzipped?
2. Does urllib2 automatically uncompress the data if it is gzipped? Will the data always be a string? | > 1. How can I tell if the data at a URL is gzipped?
This checks if the content is gzipped and decompresses it:
```
from StringIO import StringIO
import gzip
request = urllib2.Request('http://example.com/')
request.add_header('Accept-encoding', 'gzip')
response = urllib2.urlopen(request)
if response.info().get('Cont... |
Does python urllib2 automatically uncompress gzip data fetched from webpage? | 3,947,120 | 56 | 2010-10-16T00:45:48Z | 3,947,262 | 7 | 2010-10-16T01:28:21Z | [
"python",
"gzip",
"urllib2"
] | I'm using
```
data=urllib2.urlopen(url).read()
```
I want to know:
1. How can I tell if the data at a URL is gzipped?
2. Does urllib2 automatically uncompress the data if it is gzipped? Will the data always be a string? | If you are talking about a simple `.gz` file, no, urllib2 will not decode it, you will get the unchanged `.gz` file as output.
If you are talking about automatic HTTP-level compression using `Content-Encoding: gzip` or `deflate`, then that has to be deliberately requested by the client using an `Accept-Encoding` heade... |
Python script to loop through all files in directory, delete any that are less than 200 kB in size | 3,947,313 | 29 | 2010-10-16T01:46:42Z | 3,947,323 | 58 | 2010-10-16T01:52:30Z | [
"python"
] | I want to delete all files in a folder that are less than 200 kB in size.
Just want to be sure here, when i do a ls -la on my macbook, the file size says 171 or 143, I am assuming this is kb correct? | This does directory and all subdirectories:
```
import os, os.path
for root, _, files in os.walk(dirtocheck):
for f in files:
fullpath = os.path.join(root, f)
if os.path.getsize(fullpath) < 200 * 1024:
os.remove(fullpath)
```
Or:
```
import os, os.path
fileiter = (os.path.join(root,... |
Python script to loop through all files in directory, delete any that are less than 200 kB in size | 3,947,313 | 29 | 2010-10-16T01:46:42Z | 3,947,353 | 32 | 2010-10-16T02:03:20Z | [
"python"
] | I want to delete all files in a folder that are less than 200 kB in size.
Just want to be sure here, when i do a ls -la on my macbook, the file size says 171 or 143, I am assuming this is kb correct? | you can also use `find`
```
find /path -type f -size -200k -delete
``` |
Python script to loop through all files in directory, delete any that are less than 200 kB in size | 3,947,313 | 29 | 2010-10-16T01:46:42Z | 12,355,420 | 27 | 2012-09-10T16:05:21Z | [
"python"
] | I want to delete all files in a folder that are less than 200 kB in size.
Just want to be sure here, when i do a ls -la on my macbook, the file size says 171 or 143, I am assuming this is kb correct? | You could also use
```
import os
files_in_dir = os.listdir(path_to_dir)
for file_in_dir in files_in_dir:
#do the check you need on each file
``` |
Spliting a long tuple into smaller tuples | 3,947,337 | 8 | 2010-10-16T01:56:53Z | 3,947,354 | 7 | 2010-10-16T02:03:53Z | [
"python",
"list",
"split",
"tuples"
] | I have a long tuple like
```
(2, 2, 10, 10, 344, 344, 45, 43, 2, 2, 10, 10, 12, 8, 2, 10)
```
and i am trying to split it into a tuple of tuples like
```
((2, 2, 10, 10), (344, 344, 45, 43), (2, 2, 10, 10), (12, 8, 2, 10))
```
I am new to python and am not very good with tuples o(2, 2, 10, 10, 344, 344, 45, 43, 2, ... | Well there is a certain idiom for that:
```
def grouper(n, iterable):
args = [iter(iterable)] * n
return zip(*args)
t = (2, 2, 10, 10, 344, 344, 45, 43, 2, 2, 10, 10, 12, 8, 2, 10)
print grouper(4, t)
```
But its kind of complicated to explain. A slightly more general version of this is listed in [the iterto... |
Python - removing items from lists | 3,947,654 | 8 | 2010-10-16T04:16:08Z | 3,947,666 | 10 | 2010-10-16T04:22:10Z | [
"python",
"list-comprehension"
] | ```
# I have 3 lists:
L1 = [1, 2, 3, 4, 5, 6, 7, 8, 9]
L2 = [4, 7, 8]
L3 = [5, 2, 9]
# I want to create another that is L1 minus L2's memebers and L3's memebers, so:
L4 = (L1 - L2) - L3 # Of course this isn't going to work
```
I'm wondering, what is the "correct" way to do this. I can do it many different ways, but P... | Here are some tries:
```
L4 = [ n for n in L1 if (n not in L2) and (n not in L3) ] # parens for clarity
tmpset = set( L2 + L3 )
L4 = [ n for n in L1 if n not in tmpset ]
```
Now that I have had a moment to think, I realize that the `L2 + L3` thing creates a temporary list that immediately gets thrown away. So an ev... |
Python indentation when adding looping statements to existing code | 3,948,257 | 2 | 2010-10-16T09:07:35Z | 3,948,270 | 10 | 2010-10-16T09:09:12Z | [
"python",
"indentation",
"python-idle"
] | In Python, what do you do when you write 100 lines of code and forget to add a bunch of loop statements somewhere?
I mean, if you add a while statement somewhere, you've to now indent all the lines below it. It's not like you can just put braces and be done with it. Go to every single line and add tabs/spaces. What if... | I think every serious editor or IDE supports the option to select multiple lines and press tab to indent or Shift-Tab to unindent all that lines. |
How to keep all my django applications in specific folder | 3,948,356 | 19 | 2010-10-16T09:42:14Z | 3,948,368 | 11 | 2010-10-16T09:45:28Z | [
"python",
"django",
"django-apps"
] | I have a Django project, let's say "project1".
Typical folder structure for applications is:
```
/project1/
/app1/
/app2/
...
__init__.py
manage.py
settings.py
urls.py
```
What should I do if I want to hold all of my applications in some separate folder, ... | You can do this very easily, but you need to change the `settings.py` to look like this:
```
INSTALLED_APPS = (
'apps.app1',
'apps.app2',
# ...
)
```
And your `urls.py` to look like this:
```
urlpatterns = patterns('',
(r'^app1/',include('apps.app1')),
(r'^app2/',include('apps.app2')),
)... |
How to keep all my django applications in specific folder | 3,948,356 | 19 | 2010-10-16T09:42:14Z | 3,948,821 | 33 | 2010-10-16T12:09:02Z | [
"python",
"django",
"django-apps"
] | I have a Django project, let's say "project1".
Typical folder structure for applications is:
```
/project1/
/app1/
/app2/
...
__init__.py
manage.py
settings.py
urls.py
```
What should I do if I want to hold all of my applications in some separate folder, ... | You can add your `apps` folder to your python path by inserting the following in your `settings.py`:
```
import os
import sys
PROJECT_ROOT = os.path.dirname(__file__)
sys.path.insert(0, os.path.join(PROJECT_ROOT, 'apps'))
```
Then you can use all the apps in this folder just in the same way as they were in your proj... |
Is is possible to read a file from S3 in Google App Engine using boto? | 3,948,391 | 7 | 2010-10-16T09:52:44Z | 3,957,908 | 7 | 2010-10-18T09:32:11Z | [
"python",
"google-app-engine",
"amazon-s3",
"amazon-web-services",
"boto"
] | I want to manipulate a pickled python object stored in S3 in Google App Engine's sandbox. I use the suggestion in boto's [documentation](http://code.google.com/p/boto/wiki/LookupKey):
```
from boto.s3.connection import S3Connection
from boto.s3.key import Key
conn = S3Connection(config.key, config.secret_key)
bucket... | You don't need to write to a file or a StringIO at all. You can call `key.get_contents_as_string()` to return the key's contents as a string. The docs for key are [here](http://boto.cloudhackers.com/ref/s3.html#module-boto.s3.key). |
Prevent function overriding in Python | 3,948,873 | 5 | 2010-10-16T12:25:00Z | 3,948,937 | 9 | 2010-10-16T12:43:30Z | [
"python"
] | Is there any way I can prevent a child class from overriding a method in the base class?
My guess is that there is not, but I'm coming from the .NET world, and I'm trying to make my API as robust as possible, so any input is greatly appreciated.
```
class Parent:
def do_something(self):
'''This is where s... | You are right: what you are attempting is contrary to Python's structure and its culture.
Document your API, and educate your users how to use it. It's their program, so if they still want to override your function, who are you to prevent them? |
Python if statement: False vs. 0.0 | 3,948,877 | 5 | 2010-10-16T12:25:30Z | 3,948,887 | 11 | 2010-10-16T12:29:14Z | [
"python",
"if-statement"
] | Is it possible to:
```
for k,v in kwargs.items()
if v == None or v == '' or v == 1.0 or v == False:
del kwargs[k]
```
without deleting the key if v == 0.0? (False seems to equal 0.0), and without deleting the keys who equal True. | You should use `v is False` instead of `v == False`. The same applies for your comparison to `None`. See [PEP 8 - Style Guide for Python](http://www.python.org/dev/peps/pep-0008/):
> Comparisons to singletons like None should always be done with 'is' or 'is not', never the equality operators. |
Python if statement: False vs. 0.0 | 3,948,877 | 5 | 2010-10-16T12:25:30Z | 3,949,048 | 10 | 2010-10-16T13:21:02Z | [
"python",
"if-statement"
] | Is it possible to:
```
for k,v in kwargs.items()
if v == None or v == '' or v == 1.0 or v == False:
del kwargs[k]
```
without deleting the key if v == 0.0? (False seems to equal 0.0), and without deleting the keys who equal True. | Or you can put it like this :
```
if v in (None, '', 1.0) or v is False:
``` |
Why store sessions on the server instead of inside a cookie? | 3,948,975 | 7 | 2010-10-16T12:57:37Z | 3,949,032 | 14 | 2010-10-16T13:16:29Z | [
"python",
"session",
"cookies",
"flask"
] | I have been using Flask for some time now and I am really enjoying the framework. One thing that I fail to understand is that in almost all other places they talk about storing the session on the server and the session id on the client, which would then identify the session. However after using flask, I dont feel the n... | Even if your data is encrypted, the user could still roll back their cookie to a previous state (unless you start encoding one-time IDs etc)
e.g. cookie says the user has 100 credits, user spends 100 credits, they get a new cookie saying they have 0 credits. They could then restore their previous cookie (with 100 cred... |
Calculating Pearson correlation and significance in Python | 3,949,226 | 79 | 2010-10-16T14:15:27Z | 3,949,282 | 107 | 2010-10-16T14:29:57Z | [
"python",
"numpy",
"statistics",
"scipy"
] | I am looking for a function that takes as input two lists, and returns the [Pearson correlation](http://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient), and the significance of the correlation. | You can have a look at scipy: <http://docs.scipy.org/doc/scipy/reference/stats.html>
```
from pydoc import help
from scipy.stats.stats import pearsonr
help(pearsonr)
>>>
Help on function pearsonr in module scipy.stats.stats:
pearsonr(x, y)
Calculates a Pearson correlation coefficient and the p-value for testing
no... |
Calculating Pearson correlation and significance in Python | 3,949,226 | 79 | 2010-10-16T14:15:27Z | 3,949,533 | 10 | 2010-10-16T15:39:51Z | [
"python",
"numpy",
"statistics",
"scipy"
] | I am looking for a function that takes as input two lists, and returns the [Pearson correlation](http://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient), and the significance of the correlation. | Just for completeness, you can call R's statistical functions from Python using the rpy Python package. Probably overkill if all you want is the Pearson stat, but if you then want to go on and do lots of stats things that you can't find in the Python packages in other answers here, rpy might be the way to go.
www.r-pr... |
Calculating Pearson correlation and significance in Python | 3,949,226 | 79 | 2010-10-16T14:15:27Z | 5,713,856 | 24 | 2011-04-19T08:52:33Z | [
"python",
"numpy",
"statistics",
"scipy"
] | I am looking for a function that takes as input two lists, and returns the [Pearson correlation](http://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient), and the significance of the correlation. | If you don't feel like installing scipy, I've used this quick hack, slightly modified from [Programming Collective Intelligence](http://oreilly.com/catalog/9780596529321):
(Edited for correctness.)
```
from itertools import imap
def pearsonr(x, y):
# Assume len(x) == len(y)
n = len(x)
sum_x = float(sum(x))
s... |
Calculating Pearson correlation and significance in Python | 3,949,226 | 79 | 2010-10-16T14:15:27Z | 7,939,259 | 17 | 2011-10-29T13:42:11Z | [
"python",
"numpy",
"statistics",
"scipy"
] | I am looking for a function that takes as input two lists, and returns the [Pearson correlation](http://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient), and the significance of the correlation. | The following code is a straight-up interpretation of [the definition](http://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient#Definition):
```
import math
def average(x):
assert len(x) > 0
return float(sum(x)) / len(x)
def pearson_def(x, y):
assert len(x) == len(y)
n = len(x)
... |
Calculating Pearson correlation and significance in Python | 3,949,226 | 79 | 2010-10-16T14:15:27Z | 16,026,737 | 47 | 2013-04-16T00:17:58Z | [
"python",
"numpy",
"statistics",
"scipy"
] | I am looking for a function that takes as input two lists, and returns the [Pearson correlation](http://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient), and the significance of the correlation. | The Pearson correlation can be calculated with numpy's [`corrcoef`](http://docs.scipy.org/doc/numpy/reference/generated/numpy.corrcoef.html).
```
import numpy
numpy.corrcoef(list1, list2)[0, 1]
``` |
Calculating Pearson correlation and significance in Python | 3,949,226 | 79 | 2010-10-16T14:15:27Z | 17,389,980 | 8 | 2013-06-30T11:39:34Z | [
"python",
"numpy",
"statistics",
"scipy"
] | I am looking for a function that takes as input two lists, and returns the [Pearson correlation](http://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient), and the significance of the correlation. | Rather than rely on numpy/scipy, I think my answer should be the easiest to code and **understand the steps** in calculating the Pearson Correlation Coefficient (PCC) .
```
import math
# calculates the mean
def mean(x):
sum = 0.0
for i in x:
sum += i
return sum / len(x)
# calculates the sample ... |
How is set() implemented? | 3,949,310 | 57 | 2010-10-16T14:39:00Z | 3,949,350 | 48 | 2010-10-16T14:47:43Z | [
"python",
"data-structures",
"set",
"cpython"
] | I've seen people say that `set` objects in python have O(1) membership-checking. How are they implemented internally to allow this? What sort of data structure does it use? What other implications does that implementation have?
Every answer here was really enlightening, but I can only accept one, so I'll go with the c... | According to [this thread](http://groups.google.com/group/comp.lang.python/browse_thread/thread/e3e9dfdb5cbe33c8/83361c0f975add77?lnk=raot&pli=1):
> Indeed, CPython's sets are implemented as something like dictionaries
> with dummy values (the keys being the members of the set), with some
> optimization(s) that exploi... |
How is set() implemented? | 3,949,310 | 57 | 2010-10-16T14:39:00Z | 3,949,389 | 11 | 2010-10-16T14:57:26Z | [
"python",
"data-structures",
"set",
"cpython"
] | I've seen people say that `set` objects in python have O(1) membership-checking. How are they implemented internally to allow this? What sort of data structure does it use? What other implications does that implementation have?
Every answer here was really enlightening, but I can only accept one, so I'll go with the c... | I think its a common mistake, `set` lookup (or hashtable for that matter) are not O(1).
[from the Wikipedia](http://en.wikipedia.org/wiki/Hash_table#Performance_analysis)
> In the simplest model, the hash function is completely unspecified and the table does not resize. For the best possible choice of hash function,... |
How is set() implemented? | 3,949,310 | 57 | 2010-10-16T14:39:00Z | 3,949,397 | 9 | 2010-10-16T14:59:38Z | [
"python",
"data-structures",
"set",
"cpython"
] | I've seen people say that `set` objects in python have O(1) membership-checking. How are they implemented internally to allow this? What sort of data structure does it use? What other implications does that implementation have?
Every answer here was really enlightening, but I can only accept one, so I'll go with the c... | We all have easy access to [the source](http://svn.python.org/view/python/trunk/Objects/setobject.c?view=markup), where the comment preceding `set_lookkey()` says:
```
/*
The basic lookup function used by all operations.
This is based on Algorithm D from Knuth Vol. 3, Sec. 6.4.
Open addressing is preferred over chaini... |
How is set() implemented? | 3,949,310 | 57 | 2010-10-16T14:39:00Z | 3,949,795 | 47 | 2010-10-16T16:47:12Z | [
"python",
"data-structures",
"set",
"cpython"
] | I've seen people say that `set` objects in python have O(1) membership-checking. How are they implemented internally to allow this? What sort of data structure does it use? What other implications does that implementation have?
Every answer here was really enlightening, but I can only accept one, so I'll go with the c... | When people say sets have O(1) membership-checking, they are talking about the **average** case. In the **worst** case (when all hashed values collide) membership-checking is O(n). See the [Python wiki on time complexity](http://wiki.python.org/moin/TimeComplexity).
The [Wikipedia article](http://en.wikipedia.org/wiki... |
Python http download page source | 3,949,744 | 3 | 2010-10-16T16:33:48Z | 3,949,760 | 10 | 2010-10-16T16:36:21Z | [
"python",
"http"
] | hello there
i was wondering if it was possible to connect to a http host (I.e. for example google.com)
and download the source of the webpage?
Thanks in advance. | > **Using urllib2 to download a page.**
*Google will block this request as it will try to block all robots. Add user-agent to the request.*
```
import urllib2
user_agent = 'Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_4; en-US) AppleWebKit/534.3 (KHTML, like Gecko) Chrome/6.0.472.63 Safari/534.3'
headers = { 'User-... |
How to get the screen size in Tkinter? | 3,949,844 | 9 | 2010-10-16T17:02:02Z | 3,949,983 | 32 | 2010-10-16T17:33:27Z | [
"python",
"tkinter"
] | I would like to know if it is possible to calculate the screen size using tkinter.
I wanted this so that can make the program open up in the center of the screen... | ```
import tkinter as tk
root = tk.Tk()
screen_width = root.winfo_screenwidth()
screen_height = root.winfo_screenheight()
``` |
Round with integer division | 3,950,372 | 14 | 2010-10-16T19:15:39Z | 3,950,960 | 22 | 2010-10-16T21:53:55Z | [
"python",
"rounding",
"integer-division"
] | Is there is a simple, pythonic way of rounding to the nearest whole number without using floating point? I'd like to do the following but with integer arithmetic:
```
skip = int(round(1.0 * total / surplus))
```
==============
@John: Floating point is not reproducible across platforms. If you want your code to pass ... | You can do this quite simply:
`(n + d // 2) // d`, where `n` is the dividend and `d` is the divisor.
Alternatives like `(((n << 1) // d) + 1) >> 1` or the equivalent `(((n * 2) // d) + 1) // 2` may be SLOWER in recent CPythons, where an `int` is implemented like the old `long`.
The simple method does 3 variable acce... |
How to find out the current widget size in tkinter? | 3,950,687 | 7 | 2010-10-16T20:39:03Z | 3,950,766 | 17 | 2010-10-16T20:58:29Z | [
"python",
"tkinter"
] | I'm using *Python* and *Tkinter*, and I need to know the current dimensions (width, height) of a widget.
I've tried `somewidget["width"]`, but it returns only a fixed value, and is not updated whenever the widget size changes (e.g. when the window is resized). | Use `somewidget.winfo_width()` and `somewidget.winfo_height()` to get the actual widget size, the `somewidget['width']` property is only a hint given to the geometry manager. |
Safe way to uninstall old version of python | 3,950,819 | 9 | 2010-10-16T21:11:55Z | 3,951,177 | 8 | 2010-10-16T22:56:25Z | [
"python",
"osx",
"installation"
] | I want to update my Python framework on Mac and delete the old versions
but I am not sure if is safe to
```
rm -fr /Library/Frameworks/Python.framework/Versions/2.4 - 2.5 - 2.6 -3.0 etc.
```
Any suggestion? | Yes, it's safe.
The Mac's system python's are in `/System/Library/...`.
.dmg's downloaded and installed from python.org are placed in `/Library/...`.
Don't delete the /System ones, but the /Library ones are user installed, so they should be safe to delete. |
How to change email account details in appcfg.py google appengine SDK | 3,951,089 | 9 | 2010-10-16T22:29:28Z | 3,951,193 | 31 | 2010-10-16T23:03:47Z | [
"python",
"google-app-engine"
] | I have hosted GAE apps with two different email ids! When i first time used appcfg.py to `update` my app then it prompted me for email id and password but later it doesnot. How to i change the saved email id and password? I tried to use `--email=` flag with appcfg.py, but it dint worked. | Use the `--no_cookies` flag, e.g.:
```
python2.5 /path/to/google_appengine/appcfg.py --no_cookies update myapp
```
From [the documentation](http://code.google.com/appengine/docs/python/tools/uploadinganapp.html):
> --no\_cookies
>
> Do not store the administrator sign-in credentials as a cookie;
> prompt for a passw... |
How to replace the first occurrence of a regular expression in Python? | 3,951,660 | 16 | 2010-10-17T01:57:33Z | 3,951,684 | 23 | 2010-10-17T02:03:45Z | [
"python",
"regex",
"search",
"replace"
] | I want to replace just the first occurrence of a regular expression in a string. Is there a convenient way to do this? | [`re.sub()`](http://docs.python.org/library/re.html#re.sub) has a `count` parameter that indicates how many substitutions to perform. You can just set that to 1:
```
>>> s = "foo foo foofoo foo"
>>> re.sub("foo", "bar", s, 1)
'bar foo foofoo foo'
>>> s = "baz baz foo baz foo baz"
>>> re.sub("foo", "bar", s, 1)
'baz ba... |
How do you dynamically identify unknown delimiters in a data file? | 3,952,132 | 8 | 2010-10-17T05:19:37Z | 3,952,193 | 34 | 2010-10-17T05:53:00Z | [
"python",
"parsing",
"csv",
"text-files",
"textinput"
] | I have three input data files. Each uses a different delimiter for the data contained therein. Data file one looks like this:
```
apples | bananas | oranges | grapes
```
data file two looks like this:
```
quarter, dime, nickel, penny
```
data file three looks like this:
```
horse cow pig chicken goat
```
(the cha... | How about trying Python CSV's standard: <http://docs.python.org/library/csv.html#csv.Sniffer>
```
import csv
sniffer = csv.Sniffer()
dialect = sniffer.sniff('quarter, dime, nickel, penny')
print dialect.delimiter
# returns ','
``` |
Get available modules | 3,952,513 | 29 | 2010-10-17T08:13:40Z | 3,952,562 | 8 | 2010-10-17T08:37:18Z | [
"python"
] | With PHP you have the [`phpinfo()`](http://php.net/manual/en/function.phpinfo.php) which lists installed modules and then from there look up what they do.
Is there a way to see what packages/modules are installed to import? | If you use [`ipython`](http://ipython.scipy.org/), which is an improved interactive Python shell (aka "[REPL](http://en.wikipedia.org/wiki/REPL)"), you can type `importÂ` (note the space at the end) followed by a press of the `[TAB]` key to get a list of importable modules.
As noted in [this SO post](http://stackoverf... |
Get available modules | 3,952,513 | 29 | 2010-10-17T08:13:40Z | 3,952,570 | 45 | 2010-10-17T08:40:26Z | [
"python"
] | With PHP you have the [`phpinfo()`](http://php.net/manual/en/function.phpinfo.php) which lists installed modules and then from there look up what they do.
Is there a way to see what packages/modules are installed to import? | Type `help()` in the interpreter
then
```
To get a list of available modules, keywords, or topics, type "modules",
"keywords", or "topics". Each module also comes with a one-line summary
of what it does; to list the modules whose summaries contain a given word
such as "spam", type "modules spam". ... |
python and sqlite - escape input | 3,952,543 | 4 | 2010-10-17T08:27:55Z | 3,952,550 | 18 | 2010-10-17T08:30:55Z | [
"python",
"sqlite",
"pysqlite"
] | Using python with a sqlite DB - whats the method used for escaping the data going out and pulling the data coming out?
Using pysqlite2
Google has conflicting suggestions. | Use the second parameter `args` to pass arguments; don't do the escaping yourself. Not only is this easier, it also helps prevent SQL injection attacks.
```
cursor.execute(sql,args)
```
for example,
```
cursor.execute('INSERT INTO foo VALUES (?, ?)', ("It's okay", "No escaping necessary")
``` |
Extra output none while printing an command line argument | 3,953,233 | 6 | 2010-10-17T12:36:08Z | 3,953,245 | 12 | 2010-10-17T12:37:55Z | [
"python",
"function"
] | It's my day 1 of learning python. so it's a noob question for many of you. See the following code:
```
#!/usr/bin/env python
import sys
def hello(name):
name = name + '!!!!'
print 'hello', name
def main():
print hello(sys.argv[1])
if __name__ == '__main__':
main()
```
when I run it
```
$ ./Pytho... | Count the number of `print` statements in your code. You'll see that you're printing `"hello alice!!!"` in the `hello` function, *and* printing the result of the `hello` function. Because the `hello` function doesn't return a value (which you'd do with the `return` statement), it ends up returning the object `None`. Yo... |
Get a sub-set of a Python dictionary | 3,953,371 | 34 | 2010-10-17T13:25:25Z | 3,953,386 | 33 | 2010-10-17T13:28:58Z | [
"python",
"dictionary"
] | I have a dictionary:
```
{'key1':1, 'key2':2, 'key3':3}
```
I need to pass a sub-set of that dictionary to third-party code. It only wants a dictionary containing keys `['key1', 'key2', 'key99']` and if it gets another key (eg `'key3'`), it explodes in a nasty mess. The code in question is out of my control so I'm le... | ```
In [38]: adict={'key1':1, 'key2':2, 'key3':3}
In [41]: dict((k,adict[k]) for k in ('key1','key2','key99') if k in adict)
Out[41]: {'key1': 1, 'key2': 2}
```
In Python3 (or Python2.7 or later) you can do it with a [dict-comprehension](http://diveintopython3.org/comprehensions.html#dictionarycomprehension) too:
```... |
Get a sub-set of a Python dictionary | 3,953,371 | 34 | 2010-10-17T13:25:25Z | 3,953,389 | 14 | 2010-10-17T13:29:20Z | [
"python",
"dictionary"
] | I have a dictionary:
```
{'key1':1, 'key2':2, 'key3':3}
```
I need to pass a sub-set of that dictionary to third-party code. It only wants a dictionary containing keys `['key1', 'key2', 'key99']` and if it gets another key (eg `'key3'`), it explodes in a nasty mess. The code in question is out of my control so I'm le... | ```
dict(filter(lambda i:i[0] in validkeys, d.iteritems()))
``` |
Python Fibonacci Generator | 3,953,749 | 9 | 2010-10-17T15:00:53Z | 3,953,760 | 23 | 2010-10-17T15:03:18Z | [
"python",
"fibonacci",
"naming-conventions"
] | I need to make a program that asks for the amount of fibonacci numbers printed and then prints them like 0, 1, 1, 2... but I cant get it to work. My code looks the following:
```
a = int(raw_input('Give amount: '))
def fib():
a, b = 0, 1
while 1:
yield a
a, b = b, a + b
a = fib()
a.next()
0
f... | You are giving `a` too many meanings:
```
a = int(raw_input('Give amount: '))
```
vs.
```
a = fib()
```
You won't run into the problem (as often) if you give your variables more descriptive names (3 different uses of the name `a` in 10 lines of code!):
```
amount = int(raw_input('Give amount: '))
```
and change `... |
Python Fibonacci Generator | 3,953,749 | 9 | 2010-10-17T15:00:53Z | 3,954,407 | 11 | 2010-10-17T17:35:00Z | [
"python",
"fibonacci",
"naming-conventions"
] | I need to make a program that asks for the amount of fibonacci numbers printed and then prints them like 0, 1, 1, 2... but I cant get it to work. My code looks the following:
```
a = int(raw_input('Give amount: '))
def fib():
a, b = 0, 1
while 1:
yield a
a, b = b, a + b
a = fib()
a.next()
0
f... | I would use this method:
```
a = int(raw_input('Give amount: '))
def fib(n):
a, b = 0, 1
for _ in xrange(n):
yield a
a, b = b, a + b
print list(fib(a))
``` |
Python Fibonacci Generator | 3,953,749 | 9 | 2010-10-17T15:00:53Z | 3,955,269 | 10 | 2010-10-17T20:58:03Z | [
"python",
"fibonacci",
"naming-conventions"
] | I need to make a program that asks for the amount of fibonacci numbers printed and then prints them like 0, 1, 1, 2... but I cant get it to work. My code looks the following:
```
a = int(raw_input('Give amount: '))
def fib():
a, b = 0, 1
while 1:
yield a
a, b = b, a + b
a = fib()
a.next()
0
f... | Since you are writing a generator, why not use two yields, to save doing the extra shuffle?
```
import itertools as it
num_iterations = int(raw_input('How many? '))
def fib():
a,b = 0,1
while True:
yield a
b = a+b
yield b
a = a+b
for x in it.islice(fib(), num_iterations):
... |
How to make heapq evaluate the heap off of a specific attribute? | 3,954,530 | 13 | 2010-10-17T18:06:26Z | 3,954,578 | 20 | 2010-10-17T18:19:17Z | [
"python",
"data-structures",
"heap"
] | I wish to hold a heap of objects, not just numbers. They will have an integer attribute in them that the heap can sort by. The easiest way to use heaps in python is heapq, but how do I tell it to sort by a specific attribute when using heapq? | `heapq` sorts objects the same way `list.sort` does, so just define a method `__cmp__()` within your class definition, which will compare itself to another instance of the same class:
```
def __cmp__(self, other):
return cmp(self.intAttribute, other.intAttribute)
```
Works in Python 2.x.
In 3.x use:
```
def __l... |
How to make heapq evaluate the heap off of a specific attribute? | 3,954,530 | 13 | 2010-10-17T18:06:26Z | 3,954,627 | 13 | 2010-10-17T18:28:00Z | [
"python",
"data-structures",
"heap"
] | I wish to hold a heap of objects, not just numbers. They will have an integer attribute in them that the heap can sort by. The easiest way to use heaps in python is heapq, but how do I tell it to sort by a specific attribute when using heapq? | According to the example from the [documentation](https://docs.python.org/2/library/heapq.html#basic-examples), you can use tuples, and it will sort by the first element of the tuple:
```
>>> h = []
>>> heappush(h, (5, 'write code'))
>>> heappush(h, (7, 'release product'))
>>> heappush(h, (1, 'write spec'))
>>> heappu... |
Image analysis in R | 3,955,077 | 15 | 2010-10-17T20:12:36Z | 3,955,193 | 7 | 2010-10-17T20:42:39Z | [
"python",
"image",
"analysis"
] | I would like to know how I would go about performing image analysis in R. My goal is to convert images into matrices (pixel-wise information), extract/quantify color, estimate the presence of shapes and compare images based on such metrics/patterns.
I am aware of relevant packages available in Python (suggestions rele... | Also check out the RASTER package on the R-Forge website:
<http://r-forge.r-project.org/projects/raster/>
It is not released to CRAN yet but it is an excellent package to import, analyse, extract, subset images and convert them to matrices). Spatial analysis is also possible.
You can download the package in R via:
... |
Image analysis in R | 3,955,077 | 15 | 2010-10-17T20:12:36Z | 3,955,198 | 9 | 2010-10-17T20:43:52Z | [
"python",
"image",
"analysis"
] | I would like to know how I would go about performing image analysis in R. My goal is to convert images into matrices (pixel-wise information), extract/quantify color, estimate the presence of shapes and compare images based on such metrics/patterns.
I am aware of relevant packages available in Python (suggestions rele... | I'd start with `EBImage` - check out the [vignette](http://www.bioconductor.org/packages/release/bioc/vignettes/EBImage/inst/doc/EBImage-introduction.pdf) which demonstrates many of the tasks you mention. |
Django: Return 'None' from OneToOneField if related object doesn't exist? | 3,955,093 | 19 | 2010-10-17T20:15:54Z | 14,392,042 | 8 | 2013-01-18T03:43:08Z | [
"python",
"django",
"django-models"
] | I've got a Django class like this:
```
class Breakfast(m.Model):
# egg = m.OneToOneField(Egg)
...
class Egg(m.Model):
breakfast = m.OneToOneField(Breakfast, related_name="egg")
```
Is it possible to have `breakfast.egg == None` if there is no `Egg` related to the `Breakfast`?
**Edit**: Forgot to mention... | I just ran into this problem, and found an odd solution to it: if you select\_related(), then the attribute will be None if no related row exists, instead of raising an error.
```
>>> print Breakfast.objects.get(pk=1).egg
Traceback (most recent call last):
...
DoesNotExist: Egg matching query does not exist
>>> print... |
python circular imports once again (aka what's wrong with this design) | 3,955,790 | 41 | 2010-10-17T23:30:47Z | 3,956,038 | 77 | 2010-10-18T01:10:20Z | [
"python",
"design",
"dependencies",
"class-design",
"python-import"
] | Let's consider python (3.x) scripts:
main.py:
```
from test.team import team
from test.user import user
if __name__ == '__main__':
u = user()
t = team()
u.setTeam(t)
t.setLeader(u)
```
test/user.py:
```
from test.team import team
class user:
def setTeam(self, t):
if issubclass(t, team.... | Circular imports are not inherently a bad thing. It's natural for the `team` code to rely on `user` whilst the `user` does something with `team`.
The worse practice here is `from module import member`. The `team` module is trying to get the `user` class at import-time, and the `user` module is trying to get the `team`... |
How to determine bottlenecks in code, besides visual inspection? | 3,956,112 | 8 | 2010-10-18T01:39:01Z | 3,956,115 | 14 | 2010-10-18T01:40:05Z | [
"python",
"performance"
] | When visual inspection fails, how do you determine where the slowest points in your code are? Where are the bottlenecks that are ruining your runtime? | > Profile your code.
The data obtained is irrefutable in determining the performance bottlenecks.
* <http://blip.tv/pycon-us-videos-2009-2010-2011/introduction-to-python-profiling-1966784>
and the following allows you to visualize the profile data
* <http://www.vrplumber.com/programming/runsnakerun/>
> Bunch of pe... |
Python: Convert this list into dictionary | 3,956,206 | 2 | 2010-10-18T02:10:07Z | 3,956,223 | 15 | 2010-10-18T02:15:41Z | [
"python",
"list",
"dictionary",
"formatting"
] | I've got a problem , and do not know how to code in python.
I've got a `list[10, 10, 10, 20, 20, 20, 30]`
I want it be in a dictionary like this
```
{"10": 1, "20": 3, "30" : 1}
```
How could I achieve this? | ```
from collections import Counter
a = [10, 10, 10, 20, 20, 20, 30]
c = Counter(a)
# Counter({10: 3, 20: 3, 30: 1})
```
If you really want to convert the keys to strings, that's a separate step:
```
dict((str(k), v) for k, v in c.iteritems())
```
This class is new to Python 2.7; for earlier versions, use this imple... |
Minimax explained for an idiot | 3,956,258 | 9 | 2010-10-18T02:26:59Z | 3,956,356 | 15 | 2010-10-18T03:01:07Z | [
"python",
"minimax",
"tic-tac-toe"
] | I've wasted my entire day trying to use the minimax algorithm to make an unbeatable tictactoe AI. I missed something along the way (brain fried).
I'm not looking for code here, just a better explanation of where I went wrong.
### Here is my current code (the minimax method always returns 0 for some reason):
```
from... | **Step 1: Build your game tree**
Starting from the current board generate all possible moves your opponent can make.
Then for each of those generate all the possible moves you can make.
For Tic-Tac-Toe simply continue until no one can play. In other games you'll generally stop after a given time or depth.
This looks ... |
What is the PHP equivalent to Python's Try: ... Except: | 3,956,278 | 4 | 2010-10-18T02:34:50Z | 3,956,288 | 7 | 2010-10-18T02:36:23Z | [
"php",
"python",
"exception",
"try-catch"
] | I am a strong Python programmer, but not quite there when it comes to PHP. I need to try something, and if that doesn't work out, do something else.
---
**This is what it would look like in Python:**
```
try:
print "stuf"
except:
print "something else"
```
What would this be in PHP? | <http://php.net/manual/en/language.exceptions.php>
```
try {
print 'stuff';
} catch (Exception $e) {
var_dump($e);
}
```
Note: this only works for exceptions, not errors.
See <http://www.php.net/manual/en/function.set-error-handler.php> for that. |
Escaping unicode strings for MySQL in Python (avoiding exceptions.UnicodeEncodeError) | 3,956,906 | 4 | 2010-10-18T06:04:27Z | 3,956,993 | 11 | 2010-10-18T06:29:57Z | [
"python",
"mysql",
"twisted"
] | I am using Twisted to asynchronously access our database in Python. My code looks like this:
```
from twisted.enterprise import adbapi
from MySQLdb import _mysql as mysql
...
txn.execute("""
INSERT INTO users_accounts_data_snapshots (accountid, programid, fieldid, value, timestamp, jobid)
VALUES ('%s', '%s',... | Do not format strings like this. It is a massive security hole. It is not possible to do the quoting correctly by yourself. Do not try.
Use the second parameter to 'execute'. Simply put, instead of `txn.execute("... %s, %s ..." % ("xxx", "yyy"))`, do `txn.execute("... %s, %s ...", ("xxx", "yyy"))`. Notice the comma in... |
What does a audio frame contain? | 3,957,025 | 8 | 2010-10-18T06:38:34Z | 3,957,097 | 7 | 2010-10-18T06:59:53Z | [
"python",
"wav"
] | Im doing some research on how to compare sound files(wave). Basically i want to compare stored soundfiles (wav) with sound from a microphone. So in the end i would like to pre-store some voice commands of my own and then when Im running my app I would like to compare the pre-stored files with input from the microphone.... | A simple byte-by-byte comparison has almost no chance of a successful match, even with some tolerance thrown in. Voice-pattern recognition is a very complex and subtle problem that is still the subject of much research. |
What does a audio frame contain? | 3,957,025 | 8 | 2010-10-18T06:38:34Z | 3,957,230 | 25 | 2010-10-18T07:26:37Z | [
"python",
"wav"
] | Im doing some research on how to compare sound files(wave). Basically i want to compare stored soundfiles (wav) with sound from a microphone. So in the end i would like to pre-store some voice commands of my own and then when Im running my app I would like to compare the pre-stored files with input from the microphone.... | An audio frame, or sample, contains amplitude (loudness) information at that particular point in time. To produce sound, tens of thousands of frames are played in sequence to produce frequencies.
In the case of CD quality audio or uncompressed wave audio, there are around 44,100 frames/samples per second. Each of thos... |
how itertools.tee works, can type 'itertools.tee' be duplicated in order to save it's "status"? | 3,957,270 | 2 | 2010-10-18T07:34:32Z | 3,957,420 | 8 | 2010-10-18T08:04:53Z | [
"python",
"iterator",
"duplicates",
"tee"
] | All, pls see below test code about itertools.tee:
```
li = [x for x in range(10)]
ite = iter(li)
==================================================
it = itertools.tee(ite, 5)
>>> type(ite)
<type 'listiterator'>
>>> type(it)
<type 'tuple'>
>>> type(it[0])
<type 'itertools.tee'>
>... | `tee` takes over the original iterator; once you tee an iterator, discard the original iterator since the tee owns it (unless you really know what you're doing).
You can make a copy of a tee with the `copy` module:
```
import copy, itertools
it = [1,2,3,4]
a, b = itertools.tee(it)
c = copy.copy(a)
```
... or by call... |
Loading a large dictionary using python pickle | 3,957,765 | 7 | 2010-10-18T09:12:09Z | 3,957,912 | 10 | 2010-10-18T09:33:51Z | [
"python",
"pickle",
"inverted-index"
] | I have a full inverted index in form of nested python dictionary. Its structure is :
```
{word : { doc_name : [location_list] } }
```
For example let the dictionary be called index, then for a word " spam ", entry would look like :
```
{ spam : { doc1.txt : [102,300,399], doc5.txt : [200,587] } }
```
I used this st... | Try the protocol argument when using `cPickle.dump`/`cPickle.dumps`. From `cPickle.Pickler.__doc__`:
> Pickler(file, protocol=0) -- Create a pickler.
>
> This takes a file-like object for writing a pickle data stream.
> The optional proto argument tells the pickler to use the given
> protocol; supported protocols are ... |
Determine if a Python list is 95% the same? | 3,957,856 | 12 | 2010-10-18T09:24:33Z | 3,957,969 | 16 | 2010-10-18T09:39:37Z | [
"python",
"algorithm",
"list"
] | [This question](http://stackoverflow.com/questions/3787908/python-determine-if-all-items-of-a-list-are-the-same-item) asks how to determine if every element in a list is the same. How would I go about determining if 95% of the elements in a list are the same in a reasonably efficient way? For example:
```
>>> ninety_f... | ```
>>> from collections import Counter
>>> lst = [1,1,1,1,1,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1]
>>> _, freq = Counter(lst).most_common(1)[0]
>>> len(lst)*.95 <= freq
True
``` |
Determine if a Python list is 95% the same? | 3,957,856 | 12 | 2010-10-18T09:24:33Z | 3,957,979 | 15 | 2010-10-18T09:41:03Z | [
"python",
"algorithm",
"list"
] | [This question](http://stackoverflow.com/questions/3787908/python-determine-if-all-items-of-a-list-are-the-same-item) asks how to determine if every element in a list is the same. How would I go about determining if 95% of the elements in a list are the same in a reasonably efficient way? For example:
```
>>> ninety_f... | Actually, there's an easy linear solution for similar problem, only with 50% constraint instead of 95%. [Check this question](http://stackoverflow.com/questions/3740371/finding-the-max-repeated-element-in-an-array), it's just a few lines of code.
It will work for you as well, only in the end you check that selected el... |
Non biased return a list of n random positive numbers (>=0) so that their sum == total_sum | 3,959,021 | 11 | 2010-10-18T12:17:22Z | 3,959,050 | 13 | 2010-10-18T12:19:47Z | [
"python",
"algorithm"
] | I'm either looking for an algorithm or a suggestion to improve my code to generate a list of random numbers that their sum equals some arbitrary number. With my code below, it'll always be biased as the first numbers will tend to be higher.
Is there a way to have the number selection more efficient?
```
#!/usr/bin/py... | Why not just generate the right number of uniformly distributed random numbers, tot them up and scale ?
EDIT: To be a bit clearer: you want N numbers which sum to S ? So generate N uniformly distributed random numbers on the interval [0,1) or whatever your RNG produces. Add them up, they will total s (say) whereas you... |
Non biased return a list of n random positive numbers (>=0) so that their sum == total_sum | 3,959,021 | 11 | 2010-10-18T12:17:22Z | 3,959,233 | 8 | 2010-10-18T12:43:04Z | [
"python",
"algorithm"
] | I'm either looking for an algorithm or a suggestion to improve my code to generate a list of random numbers that their sum equals some arbitrary number. With my code below, it'll always be biased as the first numbers will tend to be higher.
Is there a way to have the number selection more efficient?
```
#!/usr/bin/py... | Here's how I would do it:
1. Generate n-1 random numbers, all in the range [0,`max`]
2. Sort those numbers
3. For each pair made up of the i-th and (i+1)-th number in sorted list, create an interval (i,i+1) and compute its length. The last interval will start at the last number and end at `max` and the first interval ... |
How can I make Python/Sphinx document object attributes only declared in __init__? | 3,959,615 | 8 | 2010-10-18T13:25:50Z | 3,960,105 | 7 | 2010-10-18T14:20:13Z | [
"python",
"documentation",
"attributes",
"python-sphinx",
"docstring"
] | I have Python classes with object attributes which are only declared as part of running the constructor, like so:
```
class Foo(object):
def __init__(self, base):
self.basepath = base
temp = []
for run in os.listdir(self.basepath):
if self.foo(run):
temp.append(... | > I've tried searching for a standard way to ensure that these "dynamically declared" attributes can be found (and preferably docstring'd) by the parser, but no luck so far. Any suggestions?
They cannot ever be "detected" by any parser.
Python has `setattr`. The complete set of attributes is never "detectable", in an... |
Using PIP in a virtual environment, how do I install MySQL-python | 3,960,305 | 17 | 2010-10-18T14:46:27Z | 3,960,502 | 32 | 2010-10-18T15:07:20Z | [
"python",
"ubuntu",
"virtualenv",
"pip",
"mysql-python"
] | When I'm in my virtual environment, I attempt to run:
```
pip install MySQL-python
```
This didn't work, so I tried downloading the package and installing it by running:
```
python setup.py install
```
This returns the following error:
```
% python setup.py install ... | The reason this was occurring is because I need to install the python-dev package (which I stupidly assumed had already been installed).
```
% sudo apt-get install python-dev
```
followed by
```
% pip install MySQL-python
``` |
Does Python have a module to convert CSS styles to inline styles for emails? | 3,960,721 | 5 | 2010-10-18T15:34:30Z | 5,173,388 | 11 | 2011-03-02T20:59:39Z | [
"python",
"css"
] | I know this exists in other languages, but I want it for Python to I can send emails that'll show up in GMail, etc. | I had to do the same thing a while back and put the module I made for it up on GitHub <https://github.com/rennat/pynliner> |
Python timeit problem | 3,960,834 | 5 | 2010-10-18T15:49:00Z | 3,960,896 | 16 | 2010-10-18T15:55:47Z | [
"python",
"timeit"
] | I'm trying to use the timeit module but I don't know how.
I have a main:
```
from Foo import Foo
if __name__ == '__main__':
...
foo = Foo(arg1, arg2)
t = Timer("foo.runAlgorithm()")
print t.timeit(2)
```
and my Class Foo has a method named as runAlgorithm()
the error is this:
> NameError: global name 'foo... | Instead of using the necessary [`setup` parameter](http://docs.python.org/library/timeit.html#timeit.Timer) for setting up the timeit environment, you can simply pass the method (or anything that is callable):
```
t = Timer(foo.runAlgorithm)
```
From the documentation:
> Changed in version 2.6: The stmt and setup pa... |
Passing an Array/List into Python | 3,961,007 | 17 | 2010-10-18T16:08:47Z | 3,961,058 | 23 | 2010-10-18T16:13:40Z | [
"python",
"parameter-passing",
"argument-unpacking"
] | I've been looking at passing arrays, or lists, as Python tends to call them, into a function.
I read something about using \*args, such as:
```
def someFunc(*args)
for x in args
print x
```
But not sure if this is right/wrong. Nothing seems to work as I want. I'm used to be able to pass arrays into PHP f... | When you define your function using this syntax:
```
def someFunc(*args)
for x in args
print x
```
You're telling it that you expect a variable number of arguments. If you want to pass in a List (Array from other languages) you'd do something like this:
```
def someFunc(myList = [], *args)
for x in m... |
Passing an Array/List into Python | 3,961,007 | 17 | 2010-10-18T16:08:47Z | 3,961,064 | 7 | 2010-10-18T16:14:18Z | [
"python",
"parameter-passing",
"argument-unpacking"
] | I've been looking at passing arrays, or lists, as Python tends to call them, into a function.
I read something about using \*args, such as:
```
def someFunc(*args)
for x in args
print x
```
But not sure if this is right/wrong. Nothing seems to work as I want. I'm used to be able to pass arrays into PHP f... | Python lists (which are not just arrays because their size can be changed on the fly) are normal Python objects and can be passed in to functions as any variable. The \* syntax is used for unpacking lists, which is probably not something you want to do now. |
easy_install does not work in Windows 7 | 3,961,047 | 4 | 2010-10-18T16:12:53Z | 3,961,095 | 9 | 2010-10-18T16:17:40Z | [
"python",
"pyqt4"
] | I have Python 2.6.4 installed in C:\Python26.
I have PyQt4 installed from here: <http://www.riverbankcomputing.co.uk/static/Downloads/PyQt4/PyQt-Py2.6-gpl-4.7.7-1.exe>
I have added this path to %PATH%:
```
C:\Python26;C:\Python26\Scripts
```
When I type this command in cmd.exe however:
```
easy_install cheetah
```... | I think it lives here: `c:\python\scripts\easy_install.exe`
---
Later: okay, have you installed `easy_install`? Download the appropriate Windows installer for your python version [here](http://pypi.python.org/pypi/setuptools#windows). (If you have no `scripts` directory, then you probably have not installed `easy_ins... |
Get Line Number of certain phrase in file Python | 3,961,265 | 20 | 2010-10-18T16:41:28Z | 3,961,374 | 45 | 2010-10-18T16:53:47Z | [
"python",
"file"
] | I need to get the line number of a phrase in a text file. The phrase could be:
```
the dog barked
```
I need to open the file, search it for that phrase and print the line number.
I'm using Python 2.6 on Windows XP
---
**This Is What I Have:**
```
o = open("C:/file.txt")
j = o.read()
if "the dog barked" in j:
... | ```
lookup = 'the dog barked'
with open(filename) as myFile:
for num, line in enumerate(myFile, 1):
if lookup in line:
print 'found at line:', num
``` |
GTK and PYGTK difference | 3,961,397 | 16 | 2010-10-18T16:55:50Z | 3,961,585 | 15 | 2010-10-18T17:19:32Z | [
"python",
"gtk",
"pygtk"
] | many programmers import both gtk and pygtk in this way:
```
import gtk
import pygtk
```
I have created a simple program using only gtk and it works:
```
import gtk
window = gtk.Window()
window.set_size_request(800, 700)
window.set_position(gtk.WIN_POS_CENTER)
window.connect("destroy", gtk.main_quit)
button = gtk.B... | `pygtk` is provided by `python-gobject`.
`gtk` is provided by `python-gtk2`.
`pygtk` provides the `pygtk.require` function which allows you to require that a certain version of gtk (or better) is installed. For example
```
import pygtk
pygtk.require('2.0')
```
importing `gtk` only is possible, but your program may n... |
In Python, how to display current time in readable format | 3,961,581 | 37 | 2010-10-18T17:19:06Z | 3,961,596 | 17 | 2010-10-18T17:21:07Z | [
"python",
"datetime",
"time"
] | How can I display the current time as:
```
12:18PM EST on Oct 18, 2010
```
in Python. Thanks. | All you need is [in the documentation](http://docs.python.org/library/time.html).
```
import time
time.strftime('%X %x %Z')
'16:08:12 05/08/03 AEST'
``` |
In Python, how to display current time in readable format | 3,961,581 | 37 | 2010-10-18T17:19:06Z | 3,961,739 | 46 | 2010-10-18T17:36:55Z | [
"python",
"datetime",
"time"
] | How can I display the current time as:
```
12:18PM EST on Oct 18, 2010
```
in Python. Thanks. | First the quick and dirty way, and second the precise way (recognizing daylight's savings or not).
```
import time
time.ctime() # 'Mon Oct 18 13:35:29 2010'
time.strftime('%l:%M%p %Z on %b %d, %Y') # ' 1:36PM EDT on Oct 18, 2010'
time.strftime('%l:%M%p %z on %b %d, %Y') # ' 1:36PM EST on Oct 18, 2010'
``` |
Unable to print variables in Python when using def function | 3,962,163 | 2 | 2010-10-18T18:25:56Z | 3,962,205 | 7 | 2010-10-18T18:33:05Z | [
"python"
] | I am trying to implement a simple neural net. I want to print the initial pattern, weights, activation. I then want it to print the learning process (i.e. every pattern it goes through as it learns). I am as yet unable to do this - it returns the initial and final pattern (whn I put print p in appropriate places), but ... | You have a problem with the line:
```
weights = [[[0]*n]*n]
```
When you use`*`, you multiply object references. You are using the same n-len array of zeroes every time. This will cause:
```
>>> weights[0][1][0] = 8
>>> weights
[[[8, 0, 0], [8, 0, 0], [8, 0, 0]]]
```
The first item of all the sublists is 8, because... |
How to display an image from web? | 3,962,180 | 5 | 2010-10-18T18:29:03Z | 3,962,377 | 14 | 2010-10-18T18:56:12Z | [
"python",
"gtk",
"pygtk"
] | I have written this simple script in python:
```
import gtk
window = gtk.Window()
window.set_size_request(800, 700)
window.show()
gtk.main()
```
now I want to load in this window an image from web ( and not from my PC ) like this:
<http://www.dailygalaxy.com/photos/uncategorized/2007/05/05/planet_x.jpg>
How can I... | This downloads the image from a url, but writes the data into a [gtk.gdk.Pixbuf](http://www.pygtk.org/docs/pygtk/class-gdkpixbuf.html) instead of to a file:
```
import pygtk
pygtk.require('2.0')
import gtk
import urllib2
class MainWin:
def destroy(self, widget, data=None):
print "destroy signal occurred"... |
Python: removing a TKinter frame | 3,962,247 | 3 | 2010-10-18T18:38:12Z | 3,962,726 | 8 | 2010-10-18T19:41:02Z | [
"python",
"tkinter"
] | I want to remove a frame from my interface when a specific button is clicked.
This is the invoked callback function
```
def removeMyself(self):
del self
```
However, it doesn't remove itself. I'm probably just deleting the object in python without updating the interface ?
thanks
Update
```
self.itemFrame = tk... | To remove, call either `frm.pack_forget()` or `frm.grid_forget()` depending on whether the frame was packed or grided.
Then call `frm.destroy()` if you aren't going to use it again, or hold onto the reference and repack or regrid when you want to show it again. |
How to display all words that contain these characters? | 3,962,846 | 2 | 2010-10-18T19:55:46Z | 3,962,876 | 7 | 2010-10-18T19:59:25Z | [
"python"
] | I have a text file and I want to display all words that contains both z and x characters.
How can I do that ? | Assuming you have the entire file as one large string in memory, and that the definition of a word is "a contiguous sequence of letters", then you could do something like this:
```
import re
for word in re.findall(r"\w+", mystring):
if 'x' in word and 'z' in word:
print word
``` |
How to display all words that contain these characters? | 3,962,846 | 2 | 2010-10-18T19:55:46Z | 3,962,943 | 9 | 2010-10-18T20:06:16Z | [
"python"
] | I have a text file and I want to display all words that contains both z and x characters.
How can I do that ? | If you don't want to have 2 problems:
```
for word in file('myfile.txt').read().split():
if 'x' in word and 'z' in word:
print word
``` |
Accept lowercase or uppercase letter in Python | 3,963,161 | 4 | 2010-10-18T20:35:42Z | 3,963,170 | 12 | 2010-10-18T20:37:06Z | [
"python"
] | Working on a menu display where the letter "m" takes the user back to the main menu. How can I have it so that it works regardless if the letter "m" is uppercase or lowercase?
```
elif choice == "m":
``` | One of
```
elif choice in ("m", "M"):
```
```
elif choice in "mM": # false positive if choice == ''
```
```
elif choice == 'm' or choice == 'M':
```
```
elif choice.lower() == 'm':
```
**In terms of maintainability,** the 4th alternative is better when you want to extend to case-insensitive c... |
Accept lowercase or uppercase letter in Python | 3,963,161 | 4 | 2010-10-18T20:35:42Z | 3,963,172 | 7 | 2010-10-18T20:37:08Z | [
"python"
] | Working on a menu display where the letter "m" takes the user back to the main menu. How can I have it so that it works regardless if the letter "m" is uppercase or lowercase?
```
elif choice == "m":
``` | ```
elif choice.lower() == "m":
``` |
Select between two dates with Django | 3,963,201 | 56 | 2010-10-18T20:41:30Z | 3,963,237 | 12 | 2010-10-18T20:45:14Z | [
"python",
"django"
] | I am looking to make a query that selects between dates with Django.
I know how to do this with raw SQL pretty easily, but how could this be achieved using the Django ORM?
This is where I want to add the between dates of 30 days in my query:
```
start_date = datetime.datetime.now() + datetime.timedelta(-30)
context[... | [`__range`](http://docs.djangoproject.com/en/dev/ref/models/querysets/#range) |
Select between two dates with Django | 3,963,201 | 56 | 2010-10-18T20:41:30Z | 3,963,247 | 124 | 2010-10-18T20:46:35Z | [
"python",
"django"
] | I am looking to make a query that selects between dates with Django.
I know how to do this with raw SQL pretty easily, but how could this be achieved using the Django ORM?
This is where I want to add the between dates of 30 days in my query:
```
start_date = datetime.datetime.now() + datetime.timedelta(-30)
context[... | Use the [`__range`](https://docs.djangoproject.com/en/1.7/ref/models/querysets/#range) operator:
```
...filter(current_issue__isnull=True, created_at__range=(start_date, end_date))
``` |
Convert File to HEX String Python | 3,964,245 | 16 | 2010-10-18T23:21:49Z | 3,964,285 | 27 | 2010-10-18T23:29:04Z | [
"python",
"string",
"file",
"hex"
] | How would I convert a file to a HEX string using Python? I have searched all over Google for this, but can't seem to find anything useful. | ```
import binascii
filename = 'test.dat'
with open(filename, 'rb') as f:
content = f.read()
print(binascii.hexlify(content))
``` |
Find all files in directory with extension .txt in Python | 3,964,681 | 696 | 2010-10-19T01:09:13Z | 3,964,689 | 119 | 2010-10-19T01:11:34Z | [
"python",
"file-io"
] | How can I find all files in directory with the extension `.txt` in python? | Use [glob](http://docs.python.org/library/glob.html).
```
>>> import glob
>>> glob.glob('./*.txt')
['./outline.txt', './pip-log.txt', './test.txt', './testingvim.txt']
``` |
Find all files in directory with extension .txt in Python | 3,964,681 | 696 | 2010-10-19T01:09:13Z | 3,964,690 | 74 | 2010-10-19T01:11:52Z | [
"python",
"file-io"
] | How can I find all files in directory with the extension `.txt` in python? | Something like that should do the job
```` ```
for root, dirs, files in os.walk(directory):
for file in files:
if file.endswith('.txt'):
print file
``` ```` |
Find all files in directory with extension .txt in Python | 3,964,681 | 696 | 2010-10-19T01:09:13Z | 3,964,691 | 989 | 2010-10-19T01:12:00Z | [
"python",
"file-io"
] | How can I find all files in directory with the extension `.txt` in python? | You can use [`glob`](https://docs.python.org/2/library/glob.html):
```
import glob, os
os.chdir("/mydir")
for file in glob.glob("*.txt"):
print(file)
```
or simply [`os.listdir`](https://docs.python.org/2/library/os.html#os.listdir):
```
import os
for file in os.listdir("/mydir"):
if file.endswith(".txt"):
... |
Find all files in directory with extension .txt in Python | 3,964,681 | 696 | 2010-10-19T01:09:13Z | 3,964,696 | 52 | 2010-10-19T01:13:02Z | [
"python",
"file-io"
] | How can I find all files in directory with the extension `.txt` in python? | Something like this will work:
```
>>> import os
>>> path = '/usr/share/cups/charmaps'
>>> text_files = [f for f in os.listdir(path) if f.endswith('.txt')]
>>> text_files
['euc-cn.txt', 'euc-jp.txt', 'euc-kr.txt', 'euc-tw.txt', ... 'windows-950.txt']
``` |
Find all files in directory with extension .txt in Python | 3,964,681 | 696 | 2010-10-19T01:09:13Z | 3,964,752 | 14 | 2010-10-19T01:27:09Z | [
"python",
"file-io"
] | How can I find all files in directory with the extension `.txt` in python? | I like [os.walk()](http://docs.python.org/library/os.html):
```
import os, os.path
for root, dirs, files in os.walk(dir):
for f in files:
fullpath = os.path.join(root, f)
if os.path.splitext(fullpath)[1] == '.txt':
print fullpath
```
Or with generators:
```
import os, os.path
fileit... |
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