Question

Can please someone explain how one may use ‘is’ in an ‘if’ condition. I am working with the fractions module, and I’m having some trouble:

>>> Fraction(0, 1) is 0
False
>>> float(Fraction(0, 1))
0.0
>>> float(Fraction(0,1)) is 0.0
False

The only thing I found to work is:

>>> F = Fraction(a,b)
>>> if F >= 0:
...     if F(0, 1) <= 0:
...                      ...

Is there a way to use ‘is’ here? Thanks.

Answer 1

is checks for object identity. It returns true if two names refer to the same object. One typical usecase is to check if a name refers to None:

if foo is None:
    # do stuff