Understanding Python Decorators in 12 Easy Steps!

Abstraction: Step-by-step tutorial building Python decorators from first principles

Key points:

• Builds understanding from scratch: scope rules, variable lifetimes, nested functions, first-class functions, closures, then decorators
• Functions are first-class objects in Python — they can be passed as arguments and returned as values from other functions
• Closures: inner functions remember their enclosing scope at definition time via func_closure; enables custom function factories
• A decorator is a callable that takes a function and returns a replacement function; @wrapper syntax is syntactic sugar for foo = wrapper(foo)
• *args and **kwargs enable generic decorators that can wrap functions with any signature
• @ decorator syntax introduced in Python 2.4; functools.wraps preserves the wrapped function's signature and docstring

Connections: Python · Decorators · Closures · Functional Programming

Source: http://simeonfranklin.com/blog/2012/jul/1/python-decorators-in-12-steps/