book

Head First Python, 3rd Edition

by Paul Barry

August 2023

Beginner

666 pages

15h 44m

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 did:Read MeLet’s install the latest PythonInstalling on WindowsInstalling on macOSInstalling on LinuxPython on its own is not enoughInstall the latest Jupyter Notebook backendInstall the latest release of VS CodeConfigure VS Code to your tasteAdd two required extensions to VS CodeVS Code’s Python support is state-of-the-artThe Technical Review TeamAcknowledgments
Getting ready to run some codePreparing for your first Jupyter experienceLet’s pop some code into your notebook editorPress Shift+Enter to run your codeSo… Python code really is easy to read… and runWhat if you want more than one card?Take a closer look at the card drawing codeThe Big 4: list, tuple, dictionary, and setModel your deck of cards with a setThe print dir combo mamboGetting help with dir’s outputPopulate the set with cardsThis feels like a deck of cards nowWhat exactly is “card”?Need to find something?Let’s pause and take stockPython ships with a rich standard libraryWith Python you’ll only write the code you needPython’s package ecosystem is to die forJust when you thought you were done…
How is the Coach working right now?The Coach needs a more capable stopwatchCubicle ConversationThe file and the spreadsheet are “related”Our first task: Extract the filename’s dataEverything is an object in PythonA string is an object with attributesTake a moment to appreciate what you’re looking at hereExtract the swimmer’s data from the filenameDon’t try to guess what a method does…Splitting (aka, breaking apart) a stringThere’s still some work to doRead error messages from the bottom upBe careful when combining method callsCubicle ConversationLet’s try another string methodAll that remains is to create some variablesMultiple assignment (aka unpacking)Task #1 is done!Task #2: Process the data in the file
Task #2: Process the data in the fileGrab a copy of the Coach’s dataThe open BIF works with filesCubicle ConversationUsing with to open (and close) a fileVariables are created dynamically, as neededThe file’s data is what you really wantWe have the swimmer’s data from the fileLet’s take stock of our progress so farYour new best friend, Python’s colonWhat needs to happen next feels familiarThe previous chapter is paying dividendsConverting a time string into a time valueConvert the times to hundredths of secondsTo hundredths of seconds with PythonA quick review of Python’s for loopThe gloves are off… for loops vs. while loopsYou’re cruising now and making great progress!Let’s keep a copy of the conversionsCreating a new, empty listDisplaying a list of your list’s methodsIt’s time to calculate the averageConvert the average to a swim time stringIt’s time to bring everything togetherTask #2 (finally) gets over the line!
Cubicle ConversationYou already have most of the code you needHow to create a function in PythonSave your code as often as you wishAdd the code you want to share to the functionSimply copying code is not enoughBe sure to copy all the code you needUpdate and save your code before continuing…Use modules to share codeBask in the glory of your returned dataFunctions return a tuple when requiredLet’s get a list of the Coach’s filenamesIt’s time for a bit of detective work…What can you do to lists?Is the issue with your data or your code?Cubicle ConversationDecisions, decisions, decisionsLet’s look for the colon “in” the stringDid you end up with 60 processed files?The Coach’s code is taking shape…
Cubicle ConversationCreate simple bar charts with HTML and SVGLet’s match up your HTML and SVG to the output you see on screen:Getting from a simple chart to a Coach chartBuild the strings your HTML needs in codeString concatenation doesn’t scalef-strings are a very popular Python featureGenerating SVG is easy with f-strings!The data is all there, or is it?Make sure you return all the data you needYou have numbers now, but are they usable?Scaling numeric values so they fitAll that’s left is the end of your webpageWriting to files, like reading, is painlessIt’s time to display your handiworkAll that’s left are two aesthetic tweaks…Cubicle ConversationIt’s time for another custom functionLet’s add another function to your moduleWhat’s with that hundredths value?Rounding is not what you want (in this case)One more minor formatting tweakThings are progressing well…
Get to know the data you’ll be working withLet’s extract a list of swimmers’ namesThe list-set-list duplicate removing trickThe Coach now has a list of namesA small change makes a “big” differenceEvery tuple is uniquePerform super fast lookups with dictionariesDictionaries are key/value lookup storesAnatomy of building a dictionaryDictionaries are optimized for speedy lookupDisplay the entire dictionaryThe pprint module prett y-prints your dataYour dictionary-of-lists is easily processedThis is really stating to come together

Let’s build the Coach’s webapp with FlaskInstall Flask from PyPIPrepare your folder to host your webappThe Flask MVPYou have options when working with your codeHow does your browser and your Flask-based webapp communicate?Building your webapp, bit by bit…Spoiler Alert!What’s the deal with that NameError?Cubicle ConversationFlask includes built-in session supportFlask’s session technology is a dictionaryFixing your quick fixAdjusting your code with the “better fix”Use render_template to display web pagesThat list of swimmers needs to be a drop-down listBuilding Jinja2 templates saves you timeLet’s get to know a bit about Jinja2’s markup extensions to HTMLExtend base.html to create more pagesDynamically creating a drop-down listSelecting a swimmerYou need to somehow process the form’s dataYour form’s data is available as a dictionaryYou’re inching closer to a working systemFunctions support default parameter valuesDefault parameter values are optionalThe final version of your code, 1 of 2The final version of your code, 2 of 2As a first webapp goes, this is looking goodThe Coach’s system is ready for prime time
There’s always more than one way to do somethingThere’s still something that doesn’t feel rightJinja2 executes code between {{ and }}Cubicle ConversationThe ten steps to cloud deploymentA beginner account is all you needThere’s nothing stopping you from starting…When in doubt, stick with the defaultsThe placeholder webapp doesn’t do muchDeploying your code to PythonAnywhereExtract your code in the consoleConfigure the Web tab to point to your codeEdit your webapp’s WSGI fileYour cloud-hosted webapp is ready!
The Coach needs more dataCubicle ConversationGet to know your data before scrapingWe need a plan of action…A step-by-step guide to web scrapingLet’s take the Coach’s advice and go with a three/two splitIt’s time for some HTML-parsing technologyIt’s time for some… em… eh… cold soup!Grab the raw HTML page from WikipediaGet to know your scraped dataYou can copy a slice from any sequenceIt’s time for some HTML parsing powerSearching your soup for tags of interestThe gazpacho defaults can sometimes trip you upThe returned soup is also searchableWhich table contains the data you need?Four big tables and four sets of world recordsIt’s time to extract the actual dataExtract data from all the tables, 1 of 2Extract data from all the tables, 2 of 2That nested loop did the trick!
Bending your data to your will…You now have the data you need…Apply what you already know…Is there too much data here?Filtering on the relay dataYou’re now ready to update your bar chartsCubicle ConversationPython ships with a built-in JSON libraryJSON is textual, but far from pretty“Importing” JSON dataGetting to the webapp integrationAll that’s needed: an edit and a copy’n’paste…Adding the world records to your bar chartIs your latest version of the webapp ready?But… are you really done?Cubicle ConversationPythonAnywhere has you covered…You need to upload your utility code, tooDeploy your latest webapp to PythonAnywhereTell PythonAnywhere to run your latest codeTest your utilities before cloud deploymentLet’s run your task daily at 1:00am
The elephant in the room… or is it a panda?A dictionary of dictionaries with pandas?Start by conforming to conventionA list of pandas dataframesSelecting columns from a dataframeDataframe to dictionary, attempt #1Removing unwanted data from a dataframeNegating your pandas conditonal expressionDataframe to dictionary, attempt #2Dataframe to dictionary, attempt #3It’s another dictionary of dictionariesComparing gazpacho to pandasIt was only the shortest of glimpses…
The Coach has been in touch…Cubicle ConversationIt pays to plan ahead…Task #1: Decide on your database structureThe napkin structure + dataInstalling the DBcm module from PyPIDo this to follow along…Getting started with DBcm and SQLiteDBcm works alongside the “with” statementUse triple-quoted strings for your SQLNot all SQL returns resultsCreate the events and times tablesYour tables are ready (and Task #1 is done)Determining the list of swimmer’s filesTask #2: Adding data to a database tableStay safe with Python’s SQL placeholdersLet’s repeat this process for the eventsAll that’s left is your times table…The times are in the swimmer’s files…A database update utility, 1 of 2A database update utility, 2 of 2Task #2 is (finally) done
Four queries to grab the data you needLet’s explore the queries in a new notebookFive lines of loop code become oneGetting from five lines of code to one…A nondunder combo mamboOne query down, three to go…Two queries down, two to go…The last, but not least (query)…The database utilities code, 1 of 2The database utilities code, 2 of 2Using a data module supports future refactoring activitiesIt’s nearly time for the database integrationCubicle ConversationIt’s time to integrate your database code!Updating your existing webapp’s codeReview your template(s) for changes…So… what’s the deal with your template?Let’s display a list of events…All that’s left is to draw the bar chart…Reviewing the most-recent swimclub.py codeMeet the SVG-generating Jinja2 templateCode is read more than it’s written.The convert_utils modulelist zip… what?!?Your database integrations are complete!
Cubicle ConversationMigrating to MariaDBConfiguring MariaDB for the Coach’s webappMoving the Coach’s data to MariaDBReusing your tables, 1 of 2Apply three edits to schema.sqlReusing your tables, 2 of 2Let’s check your tables are defined correctlyCopying your existing data to MariaDBMake your queries compatible with MariaDBYour database utility code need edits, tooCreate a new database on PythonAnywhereAdjust your database credentials dictionaryEdit data_utils.py to support multiple locationsCopying everything to the cloudPreparing your code and data for uploadUpdate your webapp with your latest codeJust a few more steps…Populate your cloud database with dataIt’s time for a PythonAnywhere Test DriveIs something wrong with PythonAnywhere?Cubicle ConversationThe Coach is a happy chappy!
1. ClassesIt’s not that we’re against classes…But, what if you can’t do without a custom class?What does Python class code look like?Playing cards with a class2. Exceptions3. Testing4. The walrus operator5. Where’s the switch? What switch?6. Advanced language features7. Concurrency8. Type Hints9. Virtual Environments10. ToolsProgrammer’s code editors (and IDEs)Code formattersTaking notebooks to the next level

Content preview from Head First Python, 3rd Edition

How to use this Book: Intro

Note

In this section we answer the burning question: “So why DID they put that in a Python book?”

Who is this book for?

If you can answer “yes” to all of these:

Do you already know how to program in another programming language?
Are you looking to add Python to your toolbelt so you can have a much fun coding as all those other Pythonistas?

Note

“Pythonista”: someone who loves to code with Python
Are you a learning-by-getting-your-hands-dirty type of person, preferring to do rather than listen?

This book is for you.

Who should probably back away from this book?

If you can answer “yes” to any of these:

Have you never programmed before, and can’t tell your ifs from your loops?
Are you a Python expert looking for a concise reference text for the language?
Do you hate learning new things? Do you believe no Python book, no matter how good, ...