Override .NET/Python __str__ method. #1715

Environment

• Pythonnet version: 2.5.1
• Python version: 3.6.5 64-bit.
• Operating System: Windows 10
• .NET Runtime: 4.6.1

Details

• I'm fairly noob in .NET<->Python so this is definitely not an issue, but I'm not being able to achieve what I want so any help is appreciated.

  I'm trying to monkey-patch/override (or something along these lines) a .NET class.
  My goal is to change how the __str__ method works, add some formatting to it.

  I have a .NET DLL that fires a callback with an event. This event has many attributes, one of them has the datatype System.Drawing.SizeF, so when I str(event.Size) it prints {Width=116,4981, Height=83,67346}.

  I want to change how SizeF.__str__ works, so I can format this data before returning.

• What I've tried so far

import clr
from System.Drawing import SizeF

def my_custom_str():
    # do my thing here
    pass

SizeF.__str__ = my_custom_str()

But I get AttributeError: attribute is read-only, which makes sense.

Another approach, if the code wasn't trigged by the SDK, would be to subclass SizeF:

class CustomSizeF(SizeF):
    def __str__(self, *args, **kwargs):
        # do my thing here
        pass

Then I could just use CustomSizeF. But it's the DLL that sends me this object (a very complex and nested one), so I'd have to iterate the whole object searching for SizeF instances and replace them by CustomSizeF.

Is there a way of achieving this?
Sorry if this is not the best place for asking.