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8,400 | user input and error handling average rainfall (in mmin rome months between and jan feb mar apr may jun jul aug sep oct nov dec year although this data file is very smallit is fairly typical example oftenthere are one or more header lines with information that we are not really interested in processingand the remainder... |
8,401 | print('the average rainfall for the months:'for monthvalue in zip(monthsvalues)print(monthvalueprint('the average rainfall for the year:'avgthis code is merely combination of tools and functions that we have already introduced above and in earlier so nothing is truly new notehoweverhow we skip the first line with singl... |
8,402 | user input and error handling any data to the filesimply opening it for reading will erase all its contents safer way to write to files is to use 'open(filename,' ')which will append data to the end of the file if it already existsand create new file if it does not exist for concrete exampleconsider the task of writing... |
8,403 | other sources of errors as well python has general set of tools for handling such errors that is commonly referred to as exception handlingand it used in many different programming languages to illustrate how it workslet us return to the example with the atmospheric pressure formulaimport sys from math import exp sys a... |
8,404 | user input and error handling howeverwe only handle one of the potential errorsand using if-tests to test for every possible error can lead to quite complex programs insteadit is common in python and many other languages to try to do what we intend to andif it failsto recover from the error this principle uses the try-... |
8,405 | by our code in the second casewe provide an argumentso the indexing of sys argv goes wellbut the conversion failssince python does not know how to convert the string to float this is different type of errorknown as valueerrorand we see that it is not treated very well by our except block we can improve the code by lett... |
8,406 | user input and error handling the programmer can also raise exceptions in the code abovethe exceptions were raised by standard python functionsand we wrote the code to catch them instead of just letting python raise exceptionswe can raise our own and tailor the error messages to the problem at hand we provide two examp... |
8,407 | below sea levelto around km above sea level we can therefore let the program raise valueerror for any outside this rangeeven if it does not involve python error in the usual sense the following code shows how we can use the function aboveand how we can catch and print the error message provided with the exceptions the ... |
8,408 | user input and error handling it would be convenient to make your own module that you can import into other programs when needed fortunatelythis task is very simple in pythonjust collect the functions you want in fileand you have new moduleto look at specific examplesay we want create module containing the interest for... |
8,409 | are called and used and give sensible output if we run the file with python interest py howeverif we add regular function callsprint statements and other code to the filethis code will also be run whenever we import the modulewhich is usually not what we want the solution is to add such example code in test block at th... |
8,410 | user input and error handling """return true if = within the tolerance ""return abs( btolerance success float_eq(a_computedaand float_eq( _computeda and float_eq(p_computedpand float_eq(n_computednassert success could add message here if desired if __name__ ='__main__'test_all_functions(since we have followed the namin... |
8,411 | every time we want to import modulewe can put it in the file bashrcto ensure that it is run automatically when we open new terminal window the bashrc file should be in your home directory ( '/users/sundnesbashrc')and will be listed with ls - (the dot at the start of the filename makes it hidden fileso it will not show ... |
8,412 | user input and error handling open access dieses kapitel wird unter der creative commons namensnennung international lizenz (in jeglichem medium und format erlaubtsofern sie den/die ursprunglichen autor(enund die quelle ordnungsgemass nenneneinen link zur creative commons lizenz beifugen und angebenob anderungen vorgen... |
8,413 | arrays and plotting in this we will learn to visualize mathematical functions and the results of mathematical calculations you have probably used variety of different plotting tools in the pastand we will now do much of the same thing in python the way standard plotting tools work in python is that we first compute num... |
8,414 | arrays and plotting dinates (xyin the plane or (xyzin space this concept of vectors can be generalized to any number of dimensionsand we can view vector as general -tuple of numbersv ( vn- in pythonwe could use list to represent such vectorby storing component vi as element [iin the list howevervectors are so useful an... |
8,415 | xlist [ *dx for in range( )ylist [ (xfor in xlistnow that we have the two liststhey can be sent directly to tool such as matplotlib for plottingbut before we do thiswe will introduce numpy arrays if we continue the interactive session from abovethe following lines will turn the two lists into numpy arraysimport numpy a... |
8,416 | arrays and plotting often use similar approach to create an arraybut since an array has fixed length and no append-methodwe must first create an array of the right size and then loop over it with an index to fill in the values this operation is very commonso remembering the existence of numpy' zeros function is importa... |
8,417 | import these from numpy rather than mathsince the functions in math work only with single numbers the following example illustrates how it worksfrom numpy import sinexplinspace def ( )return ** + * - def ( )return sin( )*exp(- *xx (xfloat object is float linspace( intervals in [ , (xy is array (xz is array we see thate... |
8,418 | arrays and plotting more easily by using arrays and array computations say we want to compute points on the curve described by the function (xe- sin( px) [ for [ pthe vectorized code can look as followsimport numpy as np np linspace( + np exp(- )*np sin( *np pi*xthis code is shorter and quicker to write than the one wi... |
8,419 | plt plot(xyplt show(this code is identical to the example aboveexcept for the first line and the last two lines the first line imports the plotting tools from the matplotlib packagewhich is an extensive library of functions for scientific visualization we will only use small subset of the capabilities of matplotlibmost... |
8,420 | arrays and plotting return np exp(- )*np sin( *np pi*xn np linspace( + (xplt plot(xylabel='exp(- )*sin( $\pix)'plt xlabel(' 'label on the axis plt ylabel(' 'label on the axis plt legend(mark the curve plt axis([ - ][tmintmaxyminymaxplt title('my first matplotlib demo'plt savefig('fig pdf'plt savefig('fig png'plt show(m... |
8,421 | fig example plot with more information added plt legend(plt title('plotting two curves in the same plot'plt savefig('fig_two_curves png'plt show(this example shows that the options for changing the color and plotting style of the curves are fairly intuitiveand can be easily explored by trial and error for full overview... |
8,422 | arrays and plotting exampleplotting user-specified function say we want to write small program plotf py that asks the user to provide mathematical function ( )and then plots the curve (xwe can also ask the user to specify the boundaries of the curvethat isthe lower and upper limits for an example of running the program... |
8,423 | to consider concrete examplesay we want to plot the heaviside functiondefined by ( > following the ideas from python implementation of this function could look like this def ( )if return elsereturn now we want to plot the function using the simple approach introduced above it is natural to simply create an array of val... |
8,424 | arrays and plotting plt plot( ,yplt show( variation of the same approach is to alter the (xfunction itself and put the for loop inside itdef h_loop( ) np zeros(len( )or copy(for in range(len( )) [ih( [ ]return np linspace(- + h_loop(xwe see that this last approach ensures that we can call the function with an array arg... |
8,425 | if conditionx elsex return def f_vectorized( ) np where(conditionx return this conversion is notof courseas automatic as using vectorizeand requires writing some more codebut it is much more computationally efficient than the other versions efficiency is sometimes important when working with large arrays making movie o... |
8,426 | arrays and plotting = = = - - - fig the gaussian bell function plotted for different values of let the animation run livewithout saving any files with this approachthe plots are simply drawn on the screen as they are createdthat isone plot is shown for each pass of the for loop the approach is simplebut has the disadva... |
8,427 | plot when we wanted multiple curves in single windowwhich is not what we want here insteadwe need to create an object that represents the plot and then update the -values of this object for each pass through the loop the complete code can look like import matplotlib pyplot as plt import numpy as np def (xms)return ( /(... |
8,428 | arrays and plotting herewe compute the maximum value that the function will obtain in the line max_f (mms_stop(based on either prior knowledge about the gaussian function or inspection of the mathematical expressionthis value is then used to set the axes for all the plots that make up the movie second alternativesaving... |
8,429 | the resulting gif can be played using animate from imagemagick or in browser note thatfor this approach to workone needs to be careful about the filenames the argument tmp_png passed to the convert function will simply replace with any textthereby sending all files with this pattern to convert the files are sent in lex... |
8,430 | arrays and plotting lines plt plot( , #initial plot to create the lines object def next_frame( ) (xmslines[ set_ydata(yreturn lines ani funcanimation(plt gcf()next_frameframes=s_valuesinterval= ani save('movie mp ',fps= plt show(most of the lines are identical to the examples abovebut there are some key differences we ... |
8,431 | zeros( shapex dtypeor by copying the arraya copy(or by using the convenient function zeros_likea np zeros_like(xzeros and same size as if we write function that takes either list or an array as an argumentbut inside the function it needs to be an arraywe can ensure that it is converted by using the function asarraya as... |
8,432 | arrays and plotting it is natural to use two-dimensional array ai, with the first index for the rows and the second for the columnst , , = am , am , in python codetwo-dimensional arrays are not much different from the onedimensional versionexcept for an extra index makingfillingand modifying two-dimensional array is do... |
8,433 | dictionaries and strings in this we will mainly focus on two data typesdictionaries and strings dictionaries can be considered generalization of the list data typewhere the indices are not required to be integers we have already used strings multiple times in the previous but we will revisit them here to introduce numb... |
8,434 | dictionaries and strings such an implementation is obviously not very convenient if we have large number of input and output valueshowever an alternative implementation of the mapping would be to use two lists of equal lengthwherefor instanceitem in list countries corresponds to item in list capitals howeversince such ... |
8,435 | the initialization involves defining set of key-value pairs to populate the dictionary dictionary is simply an unordered collection of such key-value pairs we are used to looping over lists to access the individual elements we can do the same with dictionarieswith the small but important difference that looping over di... |
8,436 | dictionaries and strings true deleting an element of dictionary is done exactly the same way as with listsusing the operator deland we can use len to check its lengthdel temps['oslo'remove oslo key and value temps {'paris' 'london' 'madrid' len(tempsno of key-value pairs in dict in some casesit can be useful to access ... |
8,437 | so far we have used texts (string objectsas keysbut the keys of dictionary can be any immutable (constantobject for instancewe can use integersfloatsand tuples as keysbut not lists since they are mutable objectsd { key is int { 'oslo' 'london'possible {( , ) ( ,- ) key is tuple {[ , ] [- , ] list is mutable/changeable ... |
8,438 | dictionaries and strings return sum we see that the function follows our standard recipe for evaluating sumset summation variable to zero and then add in all the terms using for loop we can write an even shorter version of the function using python' built-in function sumdef eval_poly_dict(polyx)python' sum can add elem... |
8,439 | with negative number implies counting indices from the end of the list)and extending the list representation to handle negative powers is not trivial task examplereading file data to dictionary say we have file deg txtcontaining temperature data for number of citiesoslolondonberlinparisromehelsinki we now want to read ... |
8,440 | dictionaries and strings instancewe need to know the line on which the relevant information startshow data items are separatedand how many data items are on each line the algorithm for reading and processing the text often needs to be tailored to the file structure although the split function already considered is quit... |
8,441 | lists do not have find-methodbut they have method named indexwhich is quite similar in that it searches for given element in the list and returns its index strings also have method named index that does almost the same thing as find howeverwhile find will return - if the substring does not exist in the stringindex will... |
8,442 | dictionaries and strings 'berlin at pms split(':'['berlin' at pm' split(['berlin:'' '' ''at'' ''pm'the split method has an inversecalled joinwhich is used to put list of strings together with delimiter in betweenstrings ['newton''secant''bisection''join(strings'newtonsecantbisectionnotice that we call the join method b... |
8,443 | great deal of text on multiple lines and we want to split it into single lines we can do so by using the split method with the appropriate separator for instanceon linux and mac systemssthe line separator is \nt ' st line\ nd line\ rd lineprint st line nd line rd line split('\ '[' st line'' nd line'' rd line'this examp... |
8,444 | dictionaries and strings insteadwill leave unchanged and return list of the substrings similarlya call such as replace( , does not change but it will return new string that we can assign to either or some other variable nameas we did in the example above the call replace( , does nothing useful on its ownunless it is co... |
8,445 | in this book can be accomplished with the operations listed here nearly all the tasks we encounter in this book can be solved by using combination of split and join in addition to string indexing and slicing examplereading pairs of numbers ( ,yfrom file to summarize some string operations using an exampleconsider the t... |
8,446 | dictionaries and strings open access dieses kapitel wird unter der creative commons namensnennung international lizenz (in jeglichem medium und format erlaubtsofern sie den/die ursprunglichen autor(enund die quelle ordnungsgemass nenneneinen link zur creative commons lizenz beifugen und angebenob anderungen vorgenommen... |
8,447 | classes in this we introduce classeswhich is fundamental concept in programming most modern programming languages support classes or similar conceptsand we have already encountered classes earlier in this book recallfor instancefrom how we can check the type of variable with the type functionand the output will be of t... |
8,448 | classes the same goes for more complex python classes such as lists and stringsdifferent objects contain different databut they all have the same methods the classes we create in this behave in exactly the same way first examplea class representing function to start with familiar examplewe return to the formula calcula... |
8,449 | # /( *mol#kg/mol #kpa return exp(- * * /( * )we now have function that takes single argumentbut defining as global variable is not very convenient if we want to evaluate (tfor different values of we could also set as local variable inside the function and define different functions barometric ( )barometric ( )etc for d... |
8,450 | classes define all the constants used in the formula self tself gand so on where the prefix self means that these variables become bound to the object created such bound variables are called attributes finallywe define the method valuewhich evaluates the formula using the predefined and objectbound parameters self tsel... |
8,451 | def value(selfh)return self exp(- /self in this classwe use the definition of the scale height from above and compute and store this value as an attribute inside the constructor the attribute self is then used inside the value method notice that the constants grand arein this caselocal variables in the constructorand n... |
8,452 | classes from numpy import linspace def make_table(ftstopn)for in linspace( tstopn)print(tf( )def ( )return sin( )*exp(-tmake_table( *pi send ordinary function barometric( make_table( value *pi send class method because of how (tis used inside the functionwe need to send make_table function that takes single argument ou... |
8,453 | the second line here creates new attribute new_attr for the instance of myclass such addition of attributes is entirely validbut it is rarely good programming practice since we can end up with instances of the same class having different attributes it is good habit to always equip class with constructor and to primaril... |
8,454 | classes liz olsson balance howeverthere is nothing to prevent user from changing the attributes of the account directlya first_name 'some other namea balance number ' although it can be tempting to adjust bank account balance when neededit is not the intended use of the class directly manipulating attributes in this wa... |
8,455 | way to solve the task when using code libraries developed by otherssuch conventions are risky to breaksince internal data structures can changewhile the interface to the class is more static the convention of protected variables is how programmers tell users of the class what can change and what is static library devel... |
8,456 | classes now we can call an instance of the class barometric just as any other python function baro barometric( baro( #same as baro __call__( the instance baro now behaves and looks like function the method is exactly the same as the value methodbut creating special method by renaming it to __call__ produces nicer synta... |
8,457 | / __div__(bc ** __pow__( it is naturalin most but not all casesfor these methods to return an object of the same type as the operands similarlythere are special methods for comparing objects,as followsa = __eq__(ba ! __ne__(ba __lt__(ba < __le__(ba __gt__(ba > __ge__(bthese methods should be implemented to return true ... |
8,458 | classes """return code for regenerating this instance ""return 'barometric({self })againwe can illustrate how it works in an interactive shellfrom tmp import barometric( print(bp exp(- * * /( * )) repr( 'barometric( ) eval(repr( )print( exp(- * * /( * )) the last two lines confirm that the repr method works as intended... |
8,459 | __dict__ {' ' __module__ '__main__the __doc__ attribute is the doc string we definedwhile __module__ is the name of the module to which class belongswhich is simply __main__ in this casesince we defined it in the main program howeverthe most useful item is probably __dict__which is dictionary containing the names and v... |
8,460 | classes (xf ( hf (xh for small (yet moderatehsay - this estimate will be sufficiently accurate for most applications the key parts of the implementation are to let the function be an attribute of the derivative class and then implement the numerical differentiation formula in __call__ special methodclass derivativedef ... |
8,461 | ( true test functions for classes in we introduced test functions as method to verify that our functions were implemented correctlyand the exact same approach can be used to test the implementation of classes inside the test functionwe define parameters for which we know the expected outputand then call our class metho... |
8,462 | classes the function is defined to taking one argument and also using two two local variables and that are defined outside the function before it is called howeverlooking at this code in more detail can raise questions calling dfdx( implies that derivative __call__ is calledbut how can this methods know the values of a... |
8,463 | __init__the constructorfor the line polynomial([ ,- ]__str__for doing print( __call__to enable the call ( __add__to make work __mul__to allow * in additionthe class needs method differentiate that computes the derivative of polynomialand changes it in-place starting with the most basic methodsthe constructor is fairly ... |
8,464 | classes the multiplication of two polynomials is slightly more complex than their additionso it is worth writing down the mathematics before implementing the __mul__ method the formula looks like ci xi dj xj ci dj xi+ = = = = whichin our list representationmeans that the coefficient corresponding to the power is ci dj ... |
8,465 | herethe differentiate method will change the polynomial itselfsince this is the behavior indicated by the way the function was used above we have also added separate function derivative that does not change the polynomial butinsteadreturns its derivative as new polynomial object finallylet us implement the __str__ meth... |
8,466 | object-oriented programming upon reading the titleone could wonder why object-oriented programming (oopis introduced only now we have used objects since and we started making our own classes and object types in so what is new in the answer is that the term oop can have two different meanings the first simply involves p... |
8,467 | object-oriented programming def __init__(selfc )self self def __call__(selfx)return self self * def table(selflrn)"""return table with points for < < "" 'for in np linspace(lrn) self(xs + '{ : { : }\nreturn we see that we have equipped the class with standard constructora __call__ special method for evaluating the line... |
8,468 | parabola(line)which means that parabola is subclass of line and inherits all its methods and attributes the new parabola class therefore has attributes and and three methods __init____call__and table line is base class (or parent classsuperclassand parabola is subclass (or child classderived classthe new parabola class... |
8,469 | object-oriented programming parabola( - ( print( print( table( )the real meaning of inheritance from practical viewpointand for the examples in this bookthe point of inheritance is to reuse methods and attributes from the base class and minimize code duplication on more theoretical levelinheritance should be thought of... |
8,470 | class paraboladef __init__(selfc )self self self def __call__(selfx)return self * ** self * self def table(selflrn)"""return table with points for < < "" 'for in linspace(lrn) self(xs +'% % \ (xyreturn class line(parabola)def __init__(selfc )super(__init__( notice that this version allows even more code reuse than the ... |
8,471 | object-oriented programming from math import expsinpi def ( )return exp(- )*sin( *pi*xdfdx derivative(fprint(dfdx( )howevernumerous other formulas can be used for numerical differentiationfor instance ( hf (xo( ) (xf ( ho( ) (xh ( hf ( ho( ) ( ( hf ( ( hf ( ho( ) ( ( hf ( ( hf ( hf ( ( hf ( ho( ) ( hf ( hf (xf ( ho( (x... |
8,472 | ( / )*( ( + *hf( - * ))/( *hthe problem with this code isof coursethat all the constructors are identicalso we duplicate great deal of code although the duplication of this simple constructor might not be big problemit can easily lead to errors if we want to change the constructor laterand it is therefore worth avoidin... |
8,473 | object-oriented programming from math import pisincos import numpy as np [ /( **ifor in range( )ref cos(pi/ print(fh forward central central 'for h_ in hf forward (sin,h_) central (sin,h_) central (sin,h_e abs( (pi/ )-refe abs( (pi/ )-refe abs( (pi/ )-refprint( '{h_: { : { :> { :> }' forward central central notice that... |
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8,475 | programming with design patterns james cooper boston columbus new york san francisco amsterdam cape town dubai london madrid milan munich paris montreal toronto delhi mexico city sao paulo sydney hong kong seoul singapore taipei tokyo |
8,476 | are claimed as trademarks where those designations appear in this bookand the publisher was aware of trademark claimthe designations have been printed with initial capital letters or in all capitals editor-in-chief mark taub python screenshots( - python software foundation development editor chris zahn cover imagespain... |
8,477 | pearson is dedicated to creating bias-free content that reflects the diversity of all learners we embrace the many dimensions of diversityincluding but not limited to raceethnicitygendersocioeconomic statusabilityagesexual orientationand religious or political beliefs education is powerful force for equity and change i... |
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8,479 | iintroduction introduction to objects visual programming in python visual programming of tables of data what are design patterns iicreational patterns the factory pattern the factory method pattern the abstract factory pattern the singleton pattern the builder pattern the prototype pattern summary of creational pattern... |
8,480 | chain of responsibility pattern the command pattern the interpreter pattern the iterator pattern the mediator pattern the memento pattern the observer pattern the state pattern the strategy pattern the template pattern the visitor pattern va brief introduction to python variables and syntax in python making decisions i... |
8,481 | iintroduction the tkinter library github introduction to objects the class __init__ method variables inside class collections of classes inheritance derived classes created with revised methods multiple inheritance drawing rectangle and square visibility of variables properties local variables types in python summary p... |
8,482 | adding menus to windows using the labelframe moving on examples on github visual programming of tables of data creating listbox displaying the state data using combobox the treeview widget inserting tree nodes moving on example code on github what are design patterns defining design patterns the learning process notes ... |
8,483 | contents our seeding program other factories when to use factory method programs on github the abstract factory pattern gardenmaker factory how the user interface works consequences of the abstract factory pattern thought questions code on github the singleton pattern throwing the exception creating an instance of the ... |
8,484 | iiistructural patterns the adapter pattern moving data between lists making an adapter the class adapter two-way adapters pluggable adapters programs on github the bridge pattern creating the user interface extending the bridge consequences of the bridge pattern programs on github the composite pattern an implementatio... |
8,485 | contents the dataclass decorator using dataclass with default values decoratorsadaptersand composites consequences of the decorator pattern programs on github the facade pattern building the facade classes creating databases and tables using the sqlite version consequences of the facade programs on github notes on mysq... |
8,486 | the listboxes programming help system receiving the help command the first case chain or tree kinds of requests consequences of the chain of responsibility programs on github the command pattern when to use the command pattern command objects keyboard example calling the command objects building command objects the com... |
8,487 | contents the iterator pattern why we use iterators iterators in python fibonacci iterator getting the iterator filtered iterators the iterator generator fibonacci iterator generators in classes consequences of the iterator pattern programs on github the mediator pattern an example system interactions between controls s... |
8,488 | state transitions programs on github the strategy pattern why we use the strategy pattern sample code the context the program commands the line and bar graph strategies consequences of the strategy pattern programs on github the template pattern why we use template patterns kinds of methods in template class sample cod... |
8,489 | contents va brief introduction to python variables and syntax in python data types numeric constants strings character constants variables complex numbers integer division multiple equal signs for initialization simple python program compiling and running this program arithmetic operators bitwise operators combined ari... |
8,490 | the print function formatting numbers and java style formatting the format string function -string formatting comma-separated numbers strings formatting dates using the python match function pattern matching reference moving on sample code on github development environments idle thonny pycharm visual studio other devel... |
8,491 | contents using dictionaries combining dictionaries using tuples using sets using the map function writing complete program impenetrable coding using list comprehension sample programs on github functions returning tuple where does the program start summary programs on github running python programs if you have python i... |
8,492 | when began studying pythoni was impressed by how simple coding was and how easy it was to get started writing basic programs tried several development environmentsand in all casesi was able to get simple programs running in moments the python syntax was simpleand there were no brackets or semicolons to remember other t... |
8,493 | this book is organized into five parts part "introductiondesign patterns essentially describe how objects can interact effectively this book starts by introducing objects in "introduction to objects,and providing graphical examples that clearly illustrate how the patterns work "visual programming in python,and "visual ... |
8,494 | part iii begins with short discussion of structural patterns "the adapter pattern,examines the adapter patternwhich is used to convert the programming interface of one class into that of another adapters are useful whenever you want unrelated classes to work together in single program "the bridge pattern,takes up the s... |
8,495 | the formal ways you can move through collection of data items "the mediator pattern,takes up the important mediator pattern this pattern defines how communication between objects can be simplified by using separate object to keep all objects from having to know about each other "the memento pattern,saves the internal s... |
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8,497 | must start by thanking the late john vlissidesone of the original "gang of four,for his clear explanations of several points about these design patterns he worked just few doors down from me at ibm research and didn' mind my dropping in for chat about patterns from time to time also really appreciated early supportive ... |
8,498 | james cooper holds phd in chemistry and worked in academiafor the scientific instrument industryand for ibm for yearsprimarily as computer scientist at ibm' thomas watson research center now retiredhe is the author of booksincluding on design patterns in various languages his most recent books are flameoutthe rise and ... |
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