class Foo(object):
  def bar(self):
    print 'Foo.bar'

def bar(self):
  print 'Modified bar'

Foo().bar()

Foo.bar = bar

Foo().bar()

from eventlet import patcher

# *NOTE: there might be some funny business with the "SOCKS" module
# if it even still exists
from eventlet.green import socket

patcher.inject('ftplib', globals(), ('socket', socket))

del patcher

inject函数会将eventlet的socket模块注入标准的ftplib中，globals dict被传入以做适当的修改。

让我们接着来看一下inject的实现。

__exclude = set(('__builtins__', '__file__', '__name__'))

def inject(module_name, new_globals, *additional_modules):
  """Base method for "injecting" greened modules into an imported module. It
  imports the module specified in *module_name*, arranging things so
  that the already-imported modules in *additional_modules* are used when
  *module_name* makes its imports.

  *new_globals* is either None or a globals dictionary that gets populated
  with the contents of the *module_name* module. This is useful when creating
  a "green" version of some other module.

  *additional_modules* should be a collection of two-element tuples, of the
  form (, ). If it's not specified, a default selection of
  name/module pairs is used, which should cover all use cases but may be
  slower because there are inevitably redundant or unnecessary imports.
  """
  if not additional_modules:
    # supply some defaults
    additional_modules = (
      _green_os_modules() +
      _green_select_modules() +
      _green_socket_modules() +
      _green_thread_modules() +
      _green_time_modules())

  ## Put the specified modules in sys.modules for the duration of the import
  saved = {}
  for name, mod in additional_modules:
    saved[name] = sys.modules.get(name, None)
    sys.modules[name] = mod

  ## Remove the old module from sys.modules and reimport it while
  ## the specified modules are in place
  old_module = sys.modules.pop(module_name, None)
  try:
    module = __import__(module_name, {}, {}, module_name.split('.')[:-1])

    if new_globals is not None:
      ## Update the given globals dictionary with everything from this new module
      for name in dir(module):
        if name not in __exclude:
          new_globals[name] = getattr(module, name)

    ## Keep a reference to the new module to prevent it from dying
    sys.modules['__patched_module_' + module_name] = module
  finally:
    ## Put the original module back
    if old_module is not None:
      sys.modules[module_name] = old_module
    elif module_name in sys.modules:
      del sys.modules[module_name]

    ## Put all the saved modules back
    for name, mod in additional_modules:
      if saved[name] is not None:
        sys.modules[name] = saved[name]
      else:
        del sys.modules[name]

  return module

if new_globals is not None:
  ## Update the given globals dictionary with everything from this new module
  for name in dir(module):
    if name not in __exclude:
      new_globals[name] = getattr(module, name)