New submission from Kevin <[email protected]>:
Passing a single argument as a keyword argument to a function decorated with
@functools.singledispatch results in an error:
$ python
Python 3.7.2 (default, Feb 12 2019, 08:15:36)
[Clang 10.0.0 (clang-1000.11.45.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from functools import singledispatch
>>> @singledispatch
... def f(x):
... pass
...
>>> f(x=1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<my-virtual-env>/lib/python3.7/functools.py", line 821, in wrapper
raise TypeError(f'{funcname} requires at least '
TypeError: f requires at least 1 positional argument
I think it's reasonable to expect f(x=1) to do the same as f(1) in this case.
Since there is only one argument, it should be the one passed to dispatch().
Relevant code:
def wrapper(*args, **kw):
if not args:
raise TypeError(f'{funcname} requires at least '
'1 positional argument')
return dispatch(args[0].__class__)(*args, **kw)
https://github.com/python/cpython/blob/445f1b35ce8461268438c8a6b327ddc764287e05/Lib/functools.py#L819-L824
I think the wrapper method could use something like next(iter(d.values()))
instead of args[0] when there are no args, but exactly one keyword argument.
I am happy to make the change myself
----------
components: Library (Lib)
messages: 341016
nosy: KevinG, rhettinger
priority: normal
severity: normal
status: open
title: functools.singledispatch: Shouldn't require a positional argument if
there is only one keyword argument
type: behavior
versions: Python 3.8
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Python tracker <[email protected]>
<https://bugs.python.org/issue36744>
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