Python Pocket Reference, Third Edition

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Python Pocket Reference

is roughly equivalent to the following nondecorator code:

def f(): ...

f = A(B(C(f)))

Decorators must appear on the line before a function defini-

tion, and cannot be on the same line (meaning

@A def f(): ...

is illegal). Decorators can only be applied to function defini-

tions, either at the module level or inside a class; they cannot

be applied to class definitions. Decorators also take argu-

ment lists:

@foo(1,2,3)

def f(): ...

In this case foo must be a function returning a function

(known as a metafunction).

The return Statement

return [expression]

The return statement exits the enclosing function and

returns an

expression value as the result of the call to the

function. The

expression defaults to None if it’s omitted.

Hint: return a tuple for multiple-value function results.

The yield Statement

yield expression

The yield statement suspends function state and returns an

expression. On the next iteration, the function’s prior state is

restored, and control resumes immediately after the

yield

statement. Use a return statement with no value to end the

iteration, or simply fall off the end of the function:

def generate_ints(N):

for i in xrange(N):

yield i

The yeild statement is standard as of Version 2.3 and later;

in Version 2.2, enable it with

from __future__ import

generators

.