Danny Adair - Python Cookbook - Intro

Python Cookbook - Intro

Understanding of Python's language features
Implementations of common design patterns in Python

The Arsenal

Specific solutions to specific problems
Python Language features
Design patterns
If you have a specific problem -
you know what to Google for!
What if you (think you) don't?
Better name for this series? Please tell me!

TODAY Confirming a need

Know your Python?

Descriptor
Decorator
Generator
Iterator
Meta class
List comprehension

Lambda
Set
Queue
Threading
Closure
...

Python Language Features

Highlight what's available
How to use it
When to use it

How did you start Python?

Early Pythonistas – Today's Pythonistas:
Still not the first language
Who are these people?
Veni, vidi, vici
“Reads like pseudocode” - why not have a deeper look, this seems too good to be true

Typical first Python

List comprehensions
names = [p.name for p in people if p.age>20]
Exception Handling: Easier to ask forgiveness than for permission
(famous “is string representing an integer?”)
“There's only one way to do it”
(in a python interpreter, “import this” for the Zen)

“Perfection is not when there is no more to add, but no more to take away” - Antoine de Saint-Exupery How nice!

First problems, first pitfalls

Indentation for some hard to get used to (can lead to catastrophic bugs)
Importing: a) from mymodule import *
b) relative/absolute/site-packages
Too general 'try...except:”
Standard library all over the show (PEP8 (2001) under_score/CamelCase, xmlrpc client/server (were) effectively incompatible...)
What others can you think of?

Minimalism is Appealing

Knife
Bow
Green light
Rambo is ready to roll – bring it on!
Ready to roll?

Hang on...

“Everything should be made as simple as possible, but not simpler.” - Albert Einstein

Why people ignore features

“No need, can do everything without it” (Rambo)
Existing codebase not using it, retrofitting a bi***
Production server running old Python (Remember “True = 1”?)
Core problems taken care of by library or framework (one result: Pythonic vs. Zopish)
“Too busy coding”!

Python Power Tools

I had my power drill slung low on my toolbelt and I said,“Go ahead, honey. Break something.” - Tim Allen on the challenges of figuring out what to do with a new set of general-purpose tools

Tips & Tricks Often you need one little piece of information, and no one is to blame it's not there. Some things just... need some help

Setting the Name of a Function If an outer function just returns an inner function (often a closure), the name of the returned function object is fixed, which can be confusing when the name is shown during introspection or debugging: >>> def make_adder(addend): … def adder(augend): return augend+addend … return adder … >>> plus100 = make_adder(100) >>> plus_23 = make_adder(23) >>> print plus100(1000), plus_23(1000) 1100 1023 >>> print plus100, plus_23 <function adder at 0x386530> <function adder at 0x3825f0>

Python 2.4+ You can solve the problem by setting the __name_ attribute of the inner function before returning it: def make_adder(addend): def adder(augend): return augend+addend adder._name__ = 'add_%s' % (addend, ) With this change the output becomes more useful: >>> print plus100, plus_23 <function add_100 at 0x386530> <function add_23 at 0x3825f0>

Python 2.3 Unfortunately, the __name__ attribute is read-only in this release. The same effect is achieved by constructing a new function object which differs from the other only in name: import new def make_adder(addend): def adder(augend): return augend+addend return new.function( adder.func_code, adder.func_globals, 'add_%s' % (addend,), adder.func_defaults, adder.func_closure )