book

Head First Python

by Paul Barry

November 2010

Beginner

494 pages

10h 52m

English

O'Reilly Media, Inc.

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Who is this book for?Who should probably back away from this book?We know what you’re thinkingWe know what your brain is thinkingMetacognition: thinking about thinkingHere’s what WE didHere’s what YOU can do to bend your brain into submissionRead MeThe technical review teamAcknowledgmentsSafari® Books Online
What’s to like about Python?Install Python 3Use IDLE to help learn PythonWork effectively with IDLETAB completionRecall code statementsEdit recalled codeAdjust IDLE’s preferencesDeal with complex dataCreate simple Python listsLists are like arraysAccess list data using the square bracket notationAdd more data to your listWork with your list dataIt’s time to iterateFor loops work with lists of any sizeStore lists within listsCheck a list for a listComplex data is hard to processHandle many levels of nested listsDon’t repeat code; create a functionCreate a function in PythonWhat does your function need to do?Recursion to the rescue!What a great start!Your Python Toolbox
It’s too good not to shareTurn your function into a moduleModules are everywhereComment your codePrepare your distributionBuild your distributionA quick review of your distributionImport a module to use itPython’s modules implement namespacesRegister with the PyPI websiteUpload your code to PyPIWelcome to the PyPI communityWith success comes responsibilityRequests for change are inevitableLife’s full of choicesControl behavior with an extra argumentTake your function to the next levelBefore your write new code, think BIFThe range() BIF iterates a fixed number of timesPython tries its best to run your codeTrace your codeWork out what’s wrongUpdate PyPI with your new codeYou’ve changed your APIUse optional argumentsYour module supports both APIsYour API is still not rightYour module’s reputation is restoredYour Python skills are starting to buildYour Python Toolbox
Data is external to your programIt’s all lines of textTake a closer look at the dataKnow your dataKnow your methods and ask for helpKnow your data (better)The case of the missing colonTwo very different approachesAdd extra logicHandle exceptionsTry first, then recoverThe try/except mechanismIdentify the code to protectTake a pass on the errorWhat about other errors?Handling missing filesAdd more error-checking code......Or add another level of exception handlingSo, which approach is best?Complexity is rarely a good thingYou’re done...except for one small thingBe specific with your exceptionsYour Python Toolbox

Programs produce dataOpen your file in write modeFiles are left open after an exception!Extend try with finallyKnowing the type of error is not enoughUse with to work with filesDefault formats are unsuitable for filesWhy not modify print_lol()?Pickle your dataSave with dump and restore with loadWhat if something goes wrong?Generic file I/O with pickle is the way to go!Your Python Toolbox
Coach Kelly needs your helpSort in one of two waysThe trouble with timeComprehending listsThe beauty of list comprehensionsIterate to remove duplicatesRemove duplicates with setsYour Python Toolbox
Coach Kelly is back (with a new file format)Use a dictionary to associate dataBundle your code and its data in a classDefine a classUse class to define classesCreating object instancesThe importance of selfEvery method’s first argument is selfInherit from Python’s built-in listCoach Kelly is impressedYour Python Toolbox
It’s good to shareYou’re a victim of your own successYou can put your program on the WebA “webapp” is what you wantWhat does your webapp need to do?Design your webapp with MVCModel your dataView your interfaceYATE: Yet Another Template EngineControl your codeCGI lets your web server run programsDisplay the list of athletesThe dreaded 404 error!Create another CGI scriptBut how do you know which athlete is selected?Enable CGI tracking to help with errorsA small change can make all the differenceIt’s a small change, but it’s an important oneYour webapp’s a hit!Your Python Toolbox
The world is getting smallerThere’s more than just desktop computers out thereCoach Kelly is on AndroidRun Python on the coach’s smartphoneDon’t worry about Python 2Set up your development environmentDownload the Software Development Kit (SDK)Configure the SDK and emulatorAdd an Android platformCreate a new Android Virtual Device (AVD)Install and configure Android ScriptingAdd Python to your SL4A installationTest Python on AndroidTake your Android emulator for a spinDefine your app’s requirementsThe SL4A Android APISelect from a list on AndroidThe athlete’s data CGI scriptThe complete Android app, so farThe data appears to have changed typeJSON can’t handle your custom datatypesRun your app on a real phoneStep 1: Prepare your computerStep 2: Install AndFTP on your Android phoneConfigure AndFTPThe coach is thrilled with his appWelcome to the future!Your Python Toolbox
Your athlete times app has gone nationalUse a form or dialog to accept inputCreate an HTML form templateThe data is delivered to your CGI scriptAsk for input on your Android phoneIt’s time to update your server dataAvoid race conditionsYou need a better data storage mechanismUse a database management systemPython includes SQLiteExploit Python’s database APIThe database API as Python codeA little database design goes a long wayDefine your database schemaWhat does the data look like?Transfer the data from your pickle to SQLiteWhat ID is assigned to which athlete?Insert your timing dataSQLite data management toolsIntegrate SQLite with your existing webappYou still need the list of namesGet an athlete’s details based on IDYou need to amend your Android app, tooUpdate your SQLite-based athlete dataThe NUAC is over the moon!Your Python Toolbox
There are whale sightings everywhereThe HFWWG needs to automateBuild your webapp with Google App EngineDownload and install App EngineGAE uses Python 2.5Make sure App Engine is workingApp Engine uses the MVC patternModel your data with App EngineWhat good is a model without a view?App Engine templates in an instantUse templates in App EngineDjango’s form validation frameworkCheck your formControlling your App Engine webappImprove the look of your formRestrict input by providing optionsMeet the “blank screen of death”Process the POST within your webappApp Engine handles requests as well as responsesPut your data in the datastoreDon’t break the “robustness principle”Accept almost any date and timeThere is a third optionUse “db.StringProperty()” for dates and timesIt looks like you’re not quite done yetSometimes, the tiniest change can make all the difference...Capture your user’s Google ID, tooDeploy your webapp to Google’s cloudYour HFWWG webapp is deployed!Your Python Toolbox
What’s a good time goal for the next race?So... what’s the problem?Start with the dataTake another look at the dataStore each time as a dictionaryDissect the prediction codeGet input from your userUse input() for inputGetting input raises an issue...If it’s not in the dictionary, it can’t be foundSearch for the closest matchThe trouble is with timeThe time-to-seconds-to-time moduleThe trouble is still with time...Port to AndroidYour Android app is a bunch of dialogsGet your Android app code readyPut your app together...Your app’s a wrap!And there’s no stopping you!Your Python ToolboxIt’s time to go...This is just the beginning
#1: Using a “professional” IDE#2: Coping with scoping#3: Testing#4: Advanced language features#5: Regular expressions#6: More on web frameworks#7: Object relational mappers and NoSQLThere’s NoSQL, too#8: Programming GUIs#9: Stuff to avoid#10: Other books

Content preview from Head First Python

Chapter 10. Scaling your Webapp: Getting real

The Web is a great place to host your app...until things get real. Sooner or later, you’ll hit the jackpot and your webapp will be wildly successful. When that happens, your webapp goes from a handful of hits a day to thousands, possibly tens of thousands, or even more. Will you be ready? Will your web server handle the load? How will you know? What will it cost? Who will pay? Can your data model scale to millions upon millions of data items without slowing to a crawl? Getting a webapp up and running is easy with Python and now, thanks to Google App Engine, scaling a Python webapp is achievable, too. So...flip the page and find out how.

There are whale sightings everywhere

The Head First Whale Watching Group (HFWWG) coordinates the live cetacean sightings for the entire country. To date, they’ve provided a PDF form on their website that members of the public can download, fill in, and mail to the HFWWG central office.

The form contains the essential data needed to record the sighting:

After a busy sightings weekend, the central office is swamped with completed forms for thousands of sightings...which is a data-entry nightmare as all those forms can take an age to process manually. There’s nothing worse than being stuck in front of your computer ...