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 its 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).''
 
Release 2.4.3, documentation updated on 29 March 2006.
 
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