Why can't I pass myself as a named argument to an instance method in Python?

Question

It works:

>>> def bar(x, y):
...     print x, y
...
>>> bar(y=3, x=1)
1 3

And it works:

>>> class Foo(object):
...     def bar(self, x, y):
...             print x, y
...
>>> z = Foo()
>>> z.bar(y=3, x=1)
1 3

And even this works:

>>> Foo.bar(z, y=3, x=1)
1 3

But why does this not work in Python 2.x?

>>> Foo.bar(self=z, y=3, x=1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unbound method bar() must be called with Foo instance as first argument (got nothing instead)

This complicates metaprogramming because it requires special processing. I'm curious if this is somehow necessary on the semantics of Python or just an implementation artifact.

Answer 1

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