I'm trying to replace a function defined within a class in order to modify its function (as in inner workings) without changing the actual code. I've never done this before, and, hence, am having some problems while replacing it.
Changing the code will have me accessing the package within my Python library which is not much of an option.
For example, if the module was called testMOD,
class testMOD(object): def testFunc(self, variable): var = variable self.something = var + 12
Then I would import testMOD, define a class (mytest = testMOD()), and access the defined function within the class, testFunc, and change it to already defined function.
For instance,
from somemodule import testMOD mytest = testMOD() def alternativeFunc(self, variable): var = variable self.something = var + 1.2 # A problem here mytest.testFunc = alternativeFunc
As you can see, if I just manually overwrite(?) the function in the class with my defined function it won't work properly.
It doesn't give any syntax errors, however, the problem is that the replaced function thinks that the 'self' is another variable for the function and says that it requires another argument for the 'variable' variable (I guess that wasn't a good name).
I want to make the replacing function to be exactly the same thing as the replaced function, but with additional code or some minor modifications. However, the 'self' is pretty much not working as it should be in a class.
Would there be a way to properly implement a defined function to replace a function of an imported class?
The __module__ property is intended for retrieving the module where the function was defined, either to read the source code or sometimes to re-import it in a script.
I suggest 4 solutions, from the worst to the best (IMHO), but of course it also depends on your specific constraints:
Replace the instance method (1): I use the fact that functions are descriptors in Python, so that I can use the __get__
method on AlternativeFunc
to get it as a method of the instance mytest
and overwrite the testFunc
method of the instance mytest
(without overwriting the class method):
class testMOD(object): def testFunc(self, variable): var = variable self.something = var + 12 print('Original:', self.something) def alternativeFunc1(self, variable): var = variable self.something = var + 1.2 print('Alternative1:', self.something) mytest1 = testMOD() mytest1.testFunc(10) # Original: 22 mytest1.testFunc = alternativeFunc1.__get__(mytest1, testMOD) mytest1.testFunc(10) # Alternative1: 11.2 mytestX = testMOD() mytestX.testFunc(10) # Original: 22
Replace the instance method (2): This time, I use types.MethodType
which is a bit more readable than the first solution:
import types class testMOD(object): def testFunc(self, variable): var = variable self.something = var + 12 print('Original:', self.something) def alternativeFunc1(self, variable): var = variable self.something = var + 1.2 print('Alternative1:', self.something) mytest1 = testMOD() mytest1.testFunc(10) # Original: 22 funcType = types.MethodType mytest1.testFunc = funcType(alternativeFunc1, mytest1) mytest1.testFunc(10) # Alternative1: 11.2 mytestX = testMOD() mytestX.testFunc(10) # Original: 22
Perform a monkey patching of the class method. Differently from the first method, it changes the behavior of any instance of the class:
class testMOD(object): def testFunc(self, variable): var = variable self.something = var + 12 print('Original:', self.something) def alternativeFunc2(self, variable): var = variable self.something = var + 1.2 print('Alternative2:', self.something) mytest2 = testMOD() mytest2.testFunc(10) # Original: 22 testMOD.testFunc = alternativeFunc2 mytest2.testFunc(10) # Alternative2: 11.2 mytestX = testMOD() mytestX.testFunc(10) # Alternative2: 11.2
Create a class inherited from testMOD
to override the method:
class testMODNew(testMOD): def testFunc(self, variable): var = variable self.something = var + 1.2 print('Alternative3:', self.something) mytest3 = testMODNew() mytest3.testFunc(10) # Alternative3: 11.2
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