Python Overlays: Case for Monkey Patches

Question

I am trying to wrap patch / monkey modules in python. I am trying to develop a clean way to implement this that does not interfere with the existing code.

Problem

Given a script that imports CLASSfromMODULE

from MODULE import CLASS 

I would like to replace MODULEwith another _MODULE_. Where _MODULE_is the patch for the original MODULE. The cleanest interface that I see for this is as follows.

from overlay import MODULE # Switches MODULE for _MODULE
from MODULE import CLASS   # Original import now uses _MODULE_

These are basically modules for fixing monkeys, as well as classes, functions, and methods for patch monkeys. I believe that if this is done correctly, you can consistently correct the code in a specific project.

What is the best way to implement this?

Answer 1

>>> import wrapt
>>> @wrapt.when_imported('collections')
... def hook(collections):
...     OldOrderedDict = collections.OrderedDict
...     class MyOrderedDict(OldOrderedDict):
...         def monkey(self):
...             print('ook ook')
...     collections.OrderedDict = MyOrderedDict
...     
>>> from collections import OrderedDict
>>> OrderedDict().monkey()
ook ook

Answer 2

@wim , , , , bash. /:

PACKAGE/
  overlay.py
  _decimal_.py
  __main__.py

_decimal_.py

from decimal import *
__version__ = "X.Y"

overlay.py :

import importlib
import inspect
import builtins
import os
from pathlib import Path

modsep      = '.'

class OverlayImporter(object):

 def __init__(self, *args, path = None, root = None, _import_ = __import__, **kvps):
  super().__init__(*args, **kvps)
  self.mask = "_{}_"
  self.root = Path(root or os.path.dirname(inspect.getmodule(inspect.stack()[1][0]).__file__))
  self.mods = self.modules()
  # Substitutes Import Functionality
  builtins.__import__ = self
  self.imp = _import_
  self.lom = []

 def __call__(self, name, *args) : # (self, *args, *kvps):  
  # Hooks the import statement
  if self.mapToTarget(name) in self.mods.keys() :
   if name in self.lom :
    return self.imp(name, *args)
   self.lom.append(name)
   return importlib.import_module(self.mapToTarget(name)) # This is a little black magic as we ignore the args
  return self.imp(name, *args)

 def mapToTarget(self, name) :
  """Maps request to the overlay module"""
  # Converts PACKAGE.MODULE to overlay._PACKAGE_._MODULE_
  return modsep.join([self.mask.format(part) for part in name.split(modsep)])

 def modules(self) : 
  """ Lists the overlays implemented within a directory """
  ext = '.py'
  mod = lambda parts, ext : [part[:-len(ext)] if enum + 1 == len(parts) else part for enum, part in enumerate(parts)]
  lst = [(mod(file.relative_to(self.root).parts, ext), file) for file in self.root.rglob('*'+ext)]
  return {modsep.join(item[0][:-1]) if item[0][-1] == "__init__" else modsep.join(item[0]) : item[1] for item in lst}

__main_.py

from overlay import OverlayImporter
OverlayImporter()
import decimal
print(decimal.__version__)

.