singledispatchmethod dispatches on first argument to instance-bindable method called from class level #143535
Description
In this usage of singledispatchmethod:
from functools import singledispatchmethod
class C:
@singledispatchmethod
def d(self, x):
return "base!"
@d.register(int)
def _(self, x):
return "int!"
print(C.d(C(), 1))This is what I expected in the output:
int!
But instead this was printed out:
base!
singledispatch and singledispatchmethod don't analyze and adapt argument semantics to the registered callable type, which makes them very nice and simple.
_singledispatchmethod_get always dispatches on args[0] regardless of whether it's bound or unbound, and if it didn't, that would break descriptor support; this facet is crucial for staticmethod (and classmethod) dispatches to work:
from functools import singledispatchmethod
class C:
@singledispatchmethod
@staticmethod
def d(x):
return "base!"
@d.register(int)
@staticmethod
def s(x):
return "int!"
print(C.d(1)) # int!Our tests rely on this and possibly millions of projects rely on this.
I think we could document this explicitly (and backport to 3.13 and 3.14).
Found this while working on GH-143465.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux