twisted.python.monkey.MonkeyPatcher can't patch staticmethods

	@markrwilliams reported
Trac ID	trac#9331
Type	defect
Created	2017-11-20 23:05:32Z

Sometimes it's convenient to attach a staticmethod to a class and then patch it out in a test, like so:

from twisted.trial import unittest

def free():
    print("A free function.")

class _ClassToTest(object):
    _someMethod = staticmethod(free)
    def api(self):
        self._someMethod()


class TestClass(unittest.SynchronousTestCase):
    def test_api(self):
        def fake(self):
            print("A fake.")
        self.patch(_ClassToTest, "_someMethod", fake)
    def test_broken(self):
        _ClassToTest.api()

But test_api breaks test_broken:

broken
  TestClass
    test_api ...                                                           [OK]
    test_broken ...                                                     [ERROR]

===============================================================================
[ERROR]
Traceback (most recent call last):
  File "broken.py", line 18, in test_broken
    _ClassToTest().api()
  File "broken.py", line 9, in api
    self._someMethod()
exceptions.TypeError: free() takes no arguments (1 given)

f.TestClass.test_broken
-------------------------------------------------------------------------------
Ran 2 tests in 0.015s

Because twisted.python.monkey.MonkeyPatcher.addPatch retrieves the original object with getattr and staticmethod descriptors return their wrapped free function when accessed on a class, patch can't patch staticmethods.

One solution would be to MonkeyPatch's use of getattr and setattr with __dict__ munging.

trac-id__9331 9331
type__defect defect
reporter__markrwilliams markrwilliams
priority__normal normal
milestone__None None
branch__ 
branch_author__ 
status__new new
resolution__None None
component__trial trial
keywords__None None
time__1511219132801019 1511219132801019
changetime__1511219568721385 1511219568721385
version__None None
owner__None None

Start at twisted.python.monkey.MonkeyPatcher.addPatch and reproduce the staticmethod example from the issue. Check how the original attribute is retrieved and restored, then add coverage for patching a staticmethod while preserving existing patch behavior. Done means the shown test scenario no longer receives an unexpected argument.