Python: Easy to Learn

Python: Easy to Learn Clifford French, CAS London Conference, 25 Feb 2017 Easy to misunderstand From Pycon Conference Ned Batchelder, Montreal 2015 2 May not be a very satisfactory session For some participants, too basic For some participants, too advanced For the presenter, wish I could do more Please do get in touch - [email protected] if you want a multi-session course, a one off half day or day, one to one coaching… 3 Three themes 1. Brief look behind the scenes 2. How understanding “behind the scenes” helps in the classroom 3. Speaking like a Python native and a little extra if we have time. [email protected] 4 Everything is an object Other languages use variables Key concept in Python is objects A variable is basically a name for a value No concept of declaring variables ● spring into life when needed ● removed by garbage collector when a new value is assigned to a name 5 Theme 1 - “behind the scenes” www.ranker.com 6 REPL Read Evaluate Print Loop If no name, object is swept away 7 Every object has a type and an id a = ‘pizza!’ type(a) id(a) a = 9 type (a) id(a) 8 Analogies - box, cup, aunty In some other C based languages, we declare a variable int(x) It can hold only integers - box a good analogy In Python, we don’t declare a variable and a type is dynamic We can use several names for the same value, as a person can be “aunty”, “sister”, “Ms ..” Box, cup - not good analogies in Python 9 Meet my aunties - first anna aunty Like us, this Russian doll has many names. Here she is aunty to some people Anna to others. anna Two names, one value. This doll has one id but can have many names 10 Meet another aunty - dolly This Russian doll has the name dolly. aunty The name aunty stays the same But the id is different because dolly is a different object. In Python, names are associated with values. dolly Assignment does not change value - Ned will explain more! 11 “Myths about Names and Values” Extra to watch after the conference - perhaps just 12 minutes. 12 Functions are objects Returning a value from a function is basically assigning it to a name Does this help students grasp a difficult idea? Could be a whole presentation - one example follows 13 Double and add ten or 14 How Understanding can Help 15 Using “type” function Reading text files is basic KS4 learning We will look at three approaches ❏ Using type() to understand what is happening “behind the scenes” ❏ Reading txt files from the Gutenberg project - copyright free 16 Using readlines(): Using type shows us that text is a list. We can find how many lines by using the len() function We can iterate/ cycle through it, line by line 17 It’s a list Why the double line spacing? Use print(text) to see the list: Displays each line with no end character (\n) 18 Does the type matter? This seems simpler: But this line throws a TypeError: Use type(f) to find out what sort of object f is and why the error occurs. 19 Using readline() This produces a really weird output. ● Each letter on a new line ● There are apparently 40 lines. Why? 20 Use type() to debug - diagnose Running this, we see: 21 t More sensible now to refactor ‘text’ to ‘line’ Recommended approach with ● very large files or ● with reading from an external source, eg an API or file on a website 22 So what? We can “slice” the sonnet. ❏ Slicing the list (using readlines()), we get the last line first - reverse order ❏ Slicing each line (using readline()), we get each line back to front 23 Je voudrais une tasse de cafe My school boy French is so bad, the garcon replies in English. I’m not proud of this. www.livinglanguage.com 24 Speak Python Like a Native Why? ❏ Its eezier to understood iif u rightlyk evryone els ❏ You are more likely to get help from professionals if follow conventions ❏ We need to raise the game - for further study, for careers Coding examples easy to find, eg Writing Idiomatic Python by Jeff Knupp Style conventions are in PEP8 25 Avoid comparisons with True 26 No sentry variable, no comparison with True .upper() deals with y and Y [0] takes y or Y out of Yes, Yeah, Yup, etc 27 Names for values - “variables” Always written using underscores player_name, not playerName Professional IDEs will highlight and refactor these for you ● Wing IDE ● Pycharm - for teacher or sixth form use These IDEs are free for you and your students if you email a request (www.wingware.com, www.jetbrains.com) 28 Operators - space both sides Trivial example to make the point Wing IDE can be set up to enforce spaces around operators Pycharm tests will highlight all PEP8 violations 29 But not in setting arguments to parameters You saw: Where a blank space is set to the end of each line 30 Slightly more advanced A docstring for each function ● In double quotes, with the closing double quotes on its own line ● Except for single line docstrings Two line spaces after a function 31 A Little Extra - demand Python 3.6.0 f string formatting - for me, the big win. Say goodbye to: Confusing, off- putting, irritating Welcome: Easier, neater, inclusive Also retains order in dictionaries. 32 Develop that Function 33 There are only functions There is no distinction between ● Procedures - which do not return a value ● Functions - which return a value In Python, all functions return a value If no return statement, function returns None In Python, there are no procedures, only functions 34 Want more? Propose a course ➔ from beginners ➔ to A-level Get one to one tuition or coaching Request in class support Contact: [email protected] 35 Introduction to Databases for KS4 At Camden School for Girls - Sunday 2 April £15 only 36.

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