[Python-ideas] isinstance(Decimal(), Real) -> False?

[Steven D'Aprano]

On Wed, Aug 28, 2013 at 10:25:42AM +0200, Michele Lacchia wrote:
> How can isinstance(d, Real) imply isinstance(d, Complex)? Can you elaborate
> a little more?
> It makes no sense to me, since the set of real numbers is a subset of the
> complex one.

You've just explained it. Since real numbers are a subset of complex 
numbers, every real number is a complex number with the imaginary part 
set to zero.

py> import numbers
py> isinstance(42.0, numbers.Complex)
True
py> (42.0).imag
0.0


This only applies with abstract base classes like numbers.Complex, not 
concrete classes like complex.

py> isinstance(42.0, complex)
False



-- 
Steven