2.3.2 Reserved classes of identifiers
From Python PEP
2.3.2 Reserved classes of identifiers
Certain classes of identifiers (besides keywords) have special meanings. These classes are identified by the patterns of leading and trailing underscore characters:
- Not imported by "from module import *". The special
identifier "_" is used in the interactive interpreter to store
the result of the last evaluation; it is stored in the
__builtin__ module. When not in interactive mode, "_" has no special meaning and is not defined.
See section 6.12, ``The import statement.''
Note: The name "_" is often used in conjunction with internationalization; refer to the documentation for the gettext module for more information on this convention.
- System-defined names. These names are defined by the interpreter
and it's implementation (including the standard library);
applications should not expect to define additional names using this
convention. The set of names of this class defined by Python may be
extended in future versions.
See section 3.3, ``Special method names.''
- Class-private names. Names in this category, when used within the
context of a class definition, are re-written to use a mangled form
to help avoid name clashes between ``private'' attributes of base
and derived classes.
See section 5.2.1, ``Identifiers (Names).''
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Release 2.4, documentation updated on 29 November 2004.