Monkeypatching a staticmethod?

[Roy Smith]

This is kind of surprising. I'm running Python 2.7.1. I've got a class
with a staticmethod that I want to monkeypatch with a lambda:

----------------------------------
class Foo:
@staticmethod
def x():
return 1

Foo.x = lambda: 2
print Foo.x()
----------------------------------

What's weird is that it seems to remember that x is a staticmethod
despite having been patched:

Traceback (most recent call last):
File "static.py", line 8, in <module>
Foo.x()
TypeError: unbound method <lambda>() must be called with Foo instance as
first argument (got nothing instead)

What seems to work is to patch it with another staticmethod:

----------------------------------
class Foo:
@staticmethod
def x():
return 1

@staticmethod
def x():
return 2

Foo.x = x
print Foo.x()
----------------------------------

$ python static.py
2

I didn't even know you could define a staticmethod outside of a class!

I suspect this post is really just my way of admitting that while I've
used staticmethods plenty, I've never fully understood the details of
what happens when you construct them :-)

[Ian Kelly]

On Thu, Jan 9, 2014 at 10:23 PM, Roy Smith <r...@panix.com> wrote:
> This is kind of surprising. I'm running Python 2.7.1. I've got a class
> with a staticmethod that I want to monkeypatch with a lambda:
>
> ----------------------------------
> class Foo:
> @staticmethod
> def x():
> return 1
>
> Foo.x = lambda: 2
> print Foo.x()
> ----------------------------------
>
> What's weird is that it seems to remember that x is a staticmethod
> despite having been patched:
>
> Traceback (most recent call last):
> File "static.py", line 8, in <module>
> Foo.x()
> TypeError: unbound method <lambda>() must be called with Foo instance as
> first argument (got nothing instead)

No, if it were still a staticmethod then the call would work without
error. That error is the same that you would get in Python 2 if you
defined the function directly in the class without the staticmethod
decorator. (In Python 3 the call succeeds as long as it's made from
the class and not from an instance).

> What seems to work is to patch it with another staticmethod:
>
> ----------------------------------
> class Foo:
> @staticmethod
> def x():
> return 1
>
> @staticmethod
> def x():
> return 2
>
> Foo.x = x
> print Foo.x()
> ----------------------------------
>
> $ python static.py
> 2
>
> I didn't even know you could define a staticmethod outside of a class!

I suggest defining x as a normal function and writing the assignment
as "Foo.x = staticmethod(x)" to keep x callable from the global
namespace. Or just del it after doing the monkey patch.

[Piet van Oostrum]

Ian Kelly <ian.g...@gmail.com> writes:

> I suggest defining x as a normal function and writing the assignment
> as "Foo.x = staticmethod(x)" to keep x callable from the global
> namespace. Or just del it after doing the monkey patch.

You can use Foo.x = staticmethod(lambda: 2)
--
Piet van Oostrum <pi...@vanoostrum.org>
WWW: http://pietvanoostrum.com/
PGP key: [8DAE142BE17999C4]