2.3.2 Reserved classes of identifiers

Certain classes of identifiers (besides keywords) have special meanings. These are:

Form  Meaning  Notes 
_* Not imported by "from module import *" (1)
__*__ System-defined name  
__* Class-private name mangling  

(XXX need section references here.)

Note:

(1)
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.

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