what does is ?

[Gerhard Häring]

Jonas Geiregat <kemu at sdf-eu.org> wrote:
> I saw something
> import string
> string._StringType is str
> what does this specially that IS

The "is" operator compares object *identity*, rather than equality, which the
"==" operator does.

> or in 2.2.2 string._StringTypes is str

I'd assume the check "types.StringType is str" will check if you have a Python
implementation (CPython or Jython) with class-type unification:

In pre-2.2 versions of CPython, str was a built-in function, while in 2.2+, it
is a new-style class:

    C:\>c:\Python21\python.exe
    Python 2.1.3 (#35, Apr  8 2002, 17:47:50) [MSC 32 bit (Intel)] on win32
    Type "copyright", "credits" or "license" for more information.
    >>> import types
    >>> str, types.StringType
    (<built-in function str>, <type 'string'>)
    >>>

    C:\>c:\Python22\python.exe
    Python 2.2.2 (#37, Oct 14 2002, 17:02:34) [MSC 32 bit (Intel)] on win32
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import types
    >>> str, types.StringType
    (<type 'str'>, <type 'str'>)
    >>> str is types.StringType
    1
-- 
Gerhard Häring
OPUS GmbH München
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