[Python-bugs-list] [ python-Bugs-508263 ] complex() doesn't call __complex__

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Bugs item #508263, was opened at 2002-01-24 18:22
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Category: Python Interpreter Core
Group: Python 2.2.1 candidate
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Sverker Nilsson (svenil)
Assigned to: Nobody/Anonymous (nobody)
Summary: complex() doesn't call __complex__

Initial Comment:
It calls __float__ instead.    
It is the same in 2.2b+ from Nov 7 and            
the one I got from CVS just now. /Sverker


Python 2.2+ (#1, Jan 25 2002, 03:54:26) 
[GCC 2.95.2 20000220 (Debian GNU/Linux)] on linux2
Type "help", "copyright", "credits" or "license" for
more information.
>>> import comptest
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "comptest.py", line 6, in ?
    b = complex(a)
AttributeError: Tst instance has no attribute
'__float__'
>>> 
[1]+  Stopped                 ./python
nicosys [25] cat comptest.py
class Tst:
    def __complex__(self):
        return self
    
a = Tst()
b = complex(a)



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>Comment By: Martin v. Löwis (loewis)
Date: 2002-01-25 12:00

Message:
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user_id=21627

Michael is exactly right. Python *does* call the __complex__
method of the object, as demonstrated in the attached a.py.
If the result is not a complex object, it will try to
convert it to a float, and consider this float to be the
real part of the result. This is what gives the error in
your example.

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Comment By: Michael Hudson (mwh)
Date: 2002-01-25 01:47

Message:
Logged In: YES 
user_id=6656

Um.  Why does __complex__ return self?  It has to return a
complex number, surely?

complex() calls __complex__, which doesn't return a complex
number, so it falls back to trying to convert it to a float
(which would then be promoted to complex), but this fails.

It's possible this is silly behaviour -- a
non-complex-returning __complex__ method is surely a bug and
should be flagged as such.

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