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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.