Beginner Question

Terry Reedy tjreedy at udel.edu
Mon Jan 19 23:25:01 CET 2009


K-Dawg wrote:

> I do no understand the underscore methods.

Names of the form __xyx__ are defined by the language definition and 
recognized and used by the interpreter.

See PythonLanguage / LexicalAnalysis / Identifiers / Reserved

Most refer to methods, a few to other attributes.  Modules may have 
several non-method attributes, such as '__builtins__', '__doc__', 
'__file__', '__name__', and '__package__'.

The top-level module created when the interpreter starts is given the 
name '__main__'.  If a module is imported, it __name__ is the import name.

 >>> __name__
'__main__'
 >>> import email
 >>> email.__name__
'email'
 >>> email.__file__
'C:\\Programs\\Python30\\lib\\email\\__init__.py'

If email were run directly, its name would be __main__ while the 
__file__ would be the same.

Most syntax operations have a corresponding special that implements the 
operation.  This allows user-defined objects to fully participate in 
syntax operations on an equal basis with built-in objects.

See PythonLanguage Manual / Data model / Special operations.




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