Documentation officielle de Python

2.3.1 Keywords

The following identifiers are used as reserved words, or keywords of the language, and cannot be used as ordinary identifiers. They must be spelled exactly as written here:

and       del       from      not       while    
as        elif      global    or        with     
assert    else      if        pass      yield    
break     except    import    print              
class     exec      in        raise              
continue  finally   is        return             
def       for       lambda    try

Changed in version 2.4: None became a constant and is now recognized by the compiler as a name for the built-in object None. Although it is not a keyword, you cannot assign a different object to it.

Changed in version 2.5: Both as and with are only recognized when the with_statement future feature has been enabled. It will always be enabled in Python 2.6. See section 7.5 for details. Note that using as and with as identifiers will always issue a warning, even when the with_statement future directive is not in effect.

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