monkeypatching

With the following code : import types class Foo(): def __getitem__(self, x): return x def new_get(self, x): return x + 1 x = Foo() x.__getitem__ = types.MethodType(new_get, x) x.__getitem__(42) will return 43, but x[42] will return 42. Is there a way to override __getitem__ at instance level in Python? This is unfortunately, and quite surprisingly, not allowed: For custom classes, implicit invocations of special methods are only guaranteed to work correctly if defined on an object’s type, not in the object’s instance dictionary. Source: https://docs.python.org/3/reference/datamodel.html

I was having issues while using the code of the accepted answer here . The code works depending on how I do the import of datetime. Why is that? Is it possible to mock it so it works both ways? I am using Python 3.4 . The following code illustrates the problem: import pytest from datetime import datetime mockdate = datetime(2000, 1, 1, 0, 0, 0) @pytest.fixture(autouse=True) def patch_datetime_now(monkeypatch): class mydatetime: @classmethod def now(cls): return mockdate monkeypatch.setattr('datetime.datetime', mydatetime) def test_doesnt_work(): assert datetime.now() == mockdate def test_works

I'd like to be able to add a property http://docs.python.org/library/functions.html#property to an object (a specific instance of a class). Is this possible? Some other questions about duck punching/monkey patching in python: Adding a Method to an Existing Object Instance Python: changing methods and attributes at runtime UPDATE: Answered by delnan in the comments Dynamically adding @property in python Following code works : #!/usr/bin/python class C(object): def __init__(self): self._x = None def getx(self): print "getting" return self._x def setx(self, value): print "setting" self._x = value

I don't seem to be able to monkey patch a __call__ method of class instance (and yes, I want to patch just single instances, not all of them). The following code: class A(object): def test(self): return "TEST" def __call__(self): return "EXAMPLE" a = A() print("call method: {0}".format(a.__call__)) print("test method: {0}".format(a.test)) a.__call__ = lambda : "example" a.test = lambda : "test" print("call method: {0}".format(a.__call__)) print("test method: {0}".format(a.test)) print(a()) print("Explicit call: {0}".format(a.__call__())) print(a.test()) Outputs this: call method: <bound method

Where is the best place to add a method to the integer class in Rails? I'd like to add a to_meters and to_miles methods. If you have your heart set on mucking with the Numeric (or integer, etc) class to get unit conversion, then at least do it logically and with some real value. First, create a Unit class that stores the unit type (meters,feet, cubits, etc.) and the value on creation. Then add a bunch of methods to Numeric that correspond to the valid values unit can have: these methods will return a Unit object with it's type recorded as the method name. The Unit class would support a bunch

Is it possible to add a property or a method to an object dynamically in Groovy? This is what I have tried so far: class Greet { def name Greet(who) { name = who[0].toUpperCase() + [1..-1] } def salute() { println "Hello $name!" } } g = new Greet('world') // create object g.salute() // Output "Hello World!" g.bye = { println "Goodbye, $name" } g.bye() But I get the following exception: Hello World! Caught: groovy.lang.MissingPropertyException: No such property: bye for class: Greet Possible solutions: name at test.run(greet.groovy:11) If you just want to add the bye() method to the single