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)

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