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[Python-Dev] return type of __complex__

Serhiy Storchaka storchaka at gmail.com
Sun Oct 21 10:26:19 CEST 2012 
On 21.10.12 03:15, Antoine Pitrou wrote:
> The redundancy sounds like a non-issue to me, since you can implement
> __float__ instead:

 >>> class C:
...     def __init__(self, v):
...         self.v = v
...     def __complex__(self):
...         return self.v**0.5
...
 >>> import cmath
 >>> cmath.cos(C(-1))
(1.5430806348152437-7.195794243779206e-17j)
 >>> cmath.cos(C(1))
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: __complex__ should return a complex object

Returned value can be computed and result can be float or complex 
depending on values. The author of the class with defined __complex__() 
may not even be aware that under certain circumstances he would get a float.

*Always* write "return complex(...)" is too redundant.
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