On 04.01.14 13:58, Serhiy Storchaka wrote:
Should implicit converting an instance of int, float, complex, str,
bytes, etc subclasses to call appropriate special method __int__ (or
__index__), __float__, __complex__, __str__, __bytes__, etc? Currently
explicit converting calls these methods, but implicit converting doesn't.
class I(int):
... def __int__(self): return 42
... def __index__(self): return 43
...
class F(float):
... def __float__(self): return 42.0
...
class S(str):
... def __str__(self): return '*'
...
int(I(65))
42
float(F(65))
42.0
str(S('A'))
'*'
chr(I(65))
'A'
import cmath; cmath.rect(F(65), 0)
(65+0j)
ord(S('A'))
65
Issue17576 [1] proposes to call special methods for implicit converting.
I have doubts about this.
Note that for explicit conversion this was implemented a long time ago.
See this ancient thread about str/unicode subclasses and
__str__/__unicode__:
https://mail.python.org/pipermail/python-dev/2005-January/051175.html
And this bug report:
http://bugs.python.org/issue1109424
[...]
Servus,
Walter
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