== versus is operators and type()

[Jp Calderone]

On Wed, Feb 26, 2003 at 02:31:59PM -0300, Alvaro Figueiredo wrote:
> Hi, All.
> 
> When dealing with type() function is the same to use == operator and 
> 'is' operator?
> 
> As an example, are the two expressions bellow totally equivalent?
> 
> type(arg) is type(0) or type(arg) is type(0.0)
> 
> type(arg) in (type(0), type(0.0))
> 

  Yes, short of nasty trickery, such as:

    >>> class Foo(type):
    ...   def __eq__(self, other): return False
    ...
    >>> class Bar(object):
    ...   __metaclass__ = Foo
    ...
    >>> b = Bar()
    >>> type(b) is type(b)
    True
    >>> type(b) == type(b)
    False

  Types are objects like any other, in Python.  Their normal behavior is
sane - an object compares as equal to itself - but this can be overridden.

  Jp

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