di.py

"""
My dependency injection framework for Python. Using a context manager it allows 
you to rewrite globals (such as imports, top-level classes and functions, whatever
you want) in a module and have them replaced at the end of the with block. This is
usually enough. `proxy` is just a dict-wrapping type class which will create a 
type with "class variables" for every key you give it.

Usage:
    from di import *
    
    with inject(cf.publishers, g=proxy(db=self.db)):
      for i, u in enumerate(data['urls']):
        # a function that lives in cf.publishers 
        # and depends on a global database object
        pub = next_publisher() 
        assert pub
        pubs.append(pub)
>>> 
"""

import contextlib

@contextlib.contextmanager
def inject(*mods, **data):
  orig = {}
  for mod in mods:
    for k in data.keys():
      orig[k] = getattr(mod, k)
      setattr(mod, k, data[k])
  yield
  for mod in mods:
    for k in orig.keys():
      setattr(mod, k, orig[k])

def proxy(**kv):
  return type('DictWrapper', (object,), kv)()