[Python] Why does overloading __new__ with singledispatchmethod not differentiate by type and...

I want my __new__ method to behave differently in some cases and wanted to split it into overloaded functions with singledispatchmethod.
For other methods it works like expected. However for __new__ it does not work, the overloading functions are never called. What is the reason for that?

from functools import singledispatchmethod

class Foo:
@singledispatchmethod
def __new__(cls, arg1, **kwargs):
return "default call"

@__new__.register(int)
def _(cls, arg1, **kwargs):
return "called with int " + str(arg1)

print(Foo("hi"))
# default call
print(Foo(1))
# default call


As an experiment also used singledispatch instead but without success.

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