Python Pocket Reference

Namespace and Scope Rules

• Names are created when assigned, but must exist when referenced.

• Unqualified names (“X”) deal with scopes.

• Qualified names (“object.X”) deal with object namespaces.

• Assignments in some scopes initialize object attribute namespaces (modules, classes).

Unqualified Names: Global Unless Assigned

Assignment: X = value

Makes name X local: creates or changes name X in the current local scope, unless declared global.

Reference: X

Looks for name X in the current local scope, then the current global scope, then the built-in scope.

Qualified Names: Object Namespaces

Assignment: object.X = value

Creates or alters the attribute name X in the namespace of the object being qualified.

Reference: object.X

Searches for the attribute name X in the object, then all accessible classes above it (for instances, classes).

Table 1-13. Unqualified Name Scopes

Context	Global Scope	Local Scope
Module	Same as local	The module itself
Function, method	Enclosing module	Function call
Class	Enclosing module	Class statement
Script, interactive mode	Same as local	module __main__
exec, eval	Caller’s global (or passed in)	Caller’s local (or passed in)