[New-bugs-announce] [issue45926] singledispatchmethod doesn't handle named arguments

[Alisson Oliveira]

New submission from Alisson Oliveira <a2r7o6 at gmail.com>:

`functools.singledispatchmethod` doesn't handle named arguments. Ex:

```python
from functools import singledispatchmethod

class Test:
    def __init__(self):
        ...

    @singledispatchmethod
    def get(self, filters):
        return 'Not Implemented!'

    @get.register
    def _(self, filters: dict):
        for k, v in filters.items():
            print(k, ' => ' ,  v)

    @get.register
    def _(self, filters: list):
        for f in filters:
            print(f)

if __name__ == '__main__':
    t = Test()
    t.get({'a': 'A'})
    t.get(['a'])
    t.get(filters={'a': 'A'})
```

This will raise an error:
```
a  =>  A
a
Traceback (most recent call last):
  File "/Users/alisson.oliveira/Farfetch/Git/blueprints-package/main.py", line 33, in <module>
    t.get(filters={'a': 'A'})
  File "/usr/local/Cellar/python at 3.9/3.9.9/Frameworks/Python.framework/Versions/3.9/lib/python3.9/functools.py", line 926, in _method
    method = self.dispatcher.dispatch(args[0].__class__)
IndexError: tuple index out of range
```

the problem is the lib always assume positional arguments in line 194: https://github.com/python/cpython/blob/main/Lib/functools.py#L914

----------
components: Library (Lib)
messages: 407273
nosy: alisson276
priority: normal
severity: normal
status: open
title: singledispatchmethod doesn't handle named arguments
type: behavior
versions: Python 3.10, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45926>
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