Eric V. Smith added the comment:
Oh, I don't feel my time has been wasted. Where else can I have a discussion of
__format__?
With this patch, given this:
class UpperString(str):
def __format__(self, fmt):
return str.__format__(self, fmt).upper()
class UpperEnum(UpperString, Enum):
pass
class S(UpperEnum):
a = 'a'
b = 'b'
this gives the (to me) surprising results of:
>>> format(S.a)
'S.a'
>>> format(S.a, '10')
'S.a '
>>> format(S.a, '10s')
'A '
I'd expect this to always use UpperString.__format__, since it understands all
str format specs.
And before you say UpperString is contrived, I've used classes like it in the
past: they're just like a string, but the __format__ method does something
special after calling through to str.__format__.
Which is why I think __format__ has to go in the derived type (IntEnum, in the
originally reported case): only it can decide whether to call str.__format__ or
the mix-in class's __format__.
Now, whether or not Enum needs to support such classes with specialized
__format___, I can't say. I suppose it's not super-important. But it will be
difficult to explain all of this.
Also, the patch give this:
>>> class E(IntEnum):
... one = 1
... two = 2
...
>>> format(E.one)
'E.one'
>>> format(E.one, 's')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/eric/local/python/cpython/Lib/enum.py", line 463, in __format__
return obj.__format__(val, format_spec)
ValueError: Unknown format code 's' for object of type 'int'
I can't format it using the 's' presentation type, despite the fact it looks
like a string. I think you need to add 's' to your _remove_plain_format_chars.
And consider this valid (but arguably pathological) code:
>>> format(datetime.datetime.now(), '10')
'10'
Despite this being a valid datetime format spec, your code would consider it a
str spec.
tl;dr: I think __format__ belongs in the class that understands how the
subclass handles format specs.
----------
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue18738>
_______________________________________
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
