Code blocks, execution frames, and namespaces

Introduction#

A code block is a piece of Python program text that can be executed as a unit, such as a module, a class definition or a function body. Some code blocks (like modules) are normally executed only once, others (like function bodies) may be executed many times. Code blocks may textually contain other code blocks. Code blocks may invoke other code blocks (that may or may not be textually contained in them) as part of their execution, e.g., by invoking (calling) a function.

Code block namespaces

Code Block Type	Global Namespace	Local Namespace
Module	n.s. for the module	same as global
Script (file or command)	n.s. for `__main__`	same as global
Interactive command	n.s. for `__main__`	same as global
Class definition	global n.s. of containing block	new namespace
Function body	global n.s. of containing block	new namespace
String passed to `exec` statement	global n.s. of containing block	local namespace of containing block
String passed to `eval()`	global n.s. of caller	local n.s. of caller
File read by `execfile()`	global n.s. of caller	local n.s. of caller
Expression read by `input()`	global n.s. of caller	local n.s. of caller