Python Pocket Reference, 3rd Edition

Specific Statements

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Generators and iterators

Functions containing a yield statement are compiled as

generators; when called, they return a generator object that

supports the iterator interface (i.e., a

next() method).

Iterators are objects returned by the

iter(X) built-in func-

tion; they define a

next() method, which returns the next

item in the iteration or raises a

StopIteration exception to

end the iteration.

Iteration contexts automatically use the iteration protocol to

step through collections. Classes can provide an

__iter__

method to overload the iter(X) built-in function call; if

defined, the result is used to step through objects in

for

loops, rather than the traditional __getitem__ indexing over-

load scheme.

The global Statement

global name [, name]*

The global statement is a namespace declaration: when used

inside a class or function, it treats appearances of

name as ref-

erences to a global (module-level) variable by that name—

whether it is assigned or not. Because of Python scope rules,

you need to declare only global names that are assigned

within a

def (global references are automatically found in the

enclosing module).

The import Statement

import module [, module]*

import [package.]* module [, [package.]* module]*

import [package.]* module as name [, [package.]*module as

name]*

The import statement provides module access: it imports a

module as a whole. Modules contain names fetched by quali- ...