[issue45331] Can create enum of ranges, cannot create range enum. Range should be subclassable... or EnumMeta.__new__ should be smarter.
New submission from Sam Bishop : Range types are perfectly valid as values in an enum, like so. class EnumOfRanges(Enum): ZERO = range(0, 0) RANGE_A = range(1, 11) RANGE_B = range(11, 26) However unlike the other base types , 'int', 'str', 'float', etc. You cannot create a "range enum" class RangeEnum(range, Enum): ZERO = range(0, 0) RANGE_A = range(1, 11) RANGE_B = range(11, 26) produces `TypeError: type 'range' is not an acceptable base type` when you try and import `RangeEnum`. The current documentation for `enum` implicitly says this should work by not mentioning anything special here https://docs.python.org/3/library/enum.html#others It also allows the use of range objects as value types, another implicit suggestion that we should be able to restrict an enum class to just range values like we can for other builtin class types. Also to keep this a concise issue: - Yes I'm aware not all of the base classes can be subclassed. - Yes I know I that there are good reasons bool should not be subclassable. So I'd like to suggest one of three things should be done to improve the situation: A: Solve https://bugs.python.org/issue17279 and by documenting the special base class objects that cannot be subclassed and reference this in the documentation for Enums. B: Make a decision as to which base class objects we should be able to subclass, and then improve their C implementations to allow subclassing. (It's also probably worth documenting the final list of special objects and solving https://bugs.python.org/issue17279 should this approach be selected.) C: The __new__ method on EnumMeta should be made smarter so that it either emits a more useful warning (I had to head to the CPython source code to work out what the error `TypeError: type 'range' is not an acceptable base type` meant) or somehow being more smart about how it handles the special classes which can't cannot be subclassed allowing them to be used anyway. which again sort of involves solving https://bugs.python.org/issue17279, and in the case that its just made magically smarter, I'll admit could confuse some people as to why "Enum" is special and can subclass these but their own code can't just do `class MyRange(range):` Regardless of the outcome, it would be good to fill in this pitfall one way or the other for the sake of future developers, I'm a reasonably experienced Python developer and it caught me by surprise I'm likely not the first and probably wont be the last if the behaviour remains as it currently is. -- components: Interpreter Core messages: 402960 nosy: techdragon priority: normal severity: normal status: open title: Can create enum of ranges, cannot create range enum. Range should be subclassable... or EnumMeta.__new__ should be smarter. type: enhancement versions: Python 3.9 ___ Python tracker <https://bugs.python.org/issue45331> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue34498] Python 3.7 breaks on singledispatch_function.register(pseudo_type), which Python 3.6 accepted
Sam Bishop added the comment:
Would the enhancements to resolve this, by making singledispatch accept more
things, also resolve the AssertionError from functools.singledispatch when
passing it custom types, or should I raise this as a separate issue?
from typing import NewType, List
from functools import singledispatch
@singledispatch
def fun(arg, verbose=False):
if verbose:
print("Let me just say,", end=" ")
print(arg)
MyType = NewType('MyType', List[int])
@fun.register
def _(arg: MyType , verbose=False):
if verbose:
print("Strength in numbers, eh?", end=" ")
print(arg)
---
AssertionErrorTraceback (most recent call last)
in
5
6 @fun.register
> 7 def _(arg: MyType , verbose=False):
8 if verbose:
9 print("Strength in numbers, eh?", end=" ")
~/.pyenv/versions/3.7.0/lib/python3.7/functools.py in register(cls, func)
809 argname, cls = next(iter(get_type_hints(func).items()))
810 assert isinstance(cls, type), (
--> 811 f"Invalid annotation for {argname!r}. {cls!r} is not a
class."
812 )
813 registry[cls] = func
AssertionError: Invalid annotation for 'arg'. .new_type at 0x10fcd7730> is not a class.
--
nosy: +techdragon
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[issue22790] __qualname__ missing from dir(__class__) during class initialisation
New submission from Sam Bishop:
The output of performing dir(__class__) during a class' __init__ method,
seems to be lacking the new '__qualname__' attribute in python 3.
This rough test can be pasted right into the python 3.4 REPL to see the issue.
Tested on 64bit python 3.4 running on OSX 10.9
class Foo:
class Bar(object):
keywords = dict()
def __init__(self, **kwargs):
print(dir(__class__))
print(''.join(('str(__class__.__qualname__) = ',
str(__class__.__qualname__
print(''.join((
'Is __qualname__ in the output of the dir() function? : ',
str(('__qualname__' in dir(__class__))
self.keywords = kwargs
test = Foo.Bar(see='We are missing something here')
--
components: Interpreter Core
messages: 230591
nosy: techdragon
priority: normal
severity: normal
status: open
title: __qualname__ missing from dir(__class__) during class initialisation
type: behavior
versions: Python 3.4
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[issue22790] some class attributes missing from dir(Class)
Sam Bishop added the comment: I specified 'during class initialisation' because that was the only case I confirmed. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22790 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
