import inspect

def CreateRPC(service):

  """Creates a RPC instance for the given service.

  The instance is suitable for talking to remote services.

  Each RPC instance can be used only once, and should not be reused.

  Args:

    service: string representing which service to call.

  Returns:

    the rpc object.

  Raises:

    AssertionError or RuntimeError if the stub for service doesn't supply a

    CreateRPC method.

  """

  stub = apiproxy.GetStub(service)

  assert stub, 'No api proxy found for service "%s"' % service

  assert hasattr(stub, 'CreateRPC'), ('The service "%s" doesn\'t have ' +

                                      'a CreateRPC method.' % service)

  return stub.CreateRPC()

  """The APIProxy entry point for a synchronous API call.

  apiproxy.MakeSyncCall(service, call, request, response)

class ListOfHooks(object):

  """An ordered collection of hooks for a particular API call.

  A hook is a function that has exactly the same signature as

  a service stub. It will be called before or after an api hook is

  executed, depending on whether this list is for precall of postcall hooks.

  Hooks can be used for debugging purposes (check certain

  pre- or postconditions on api calls) or to apply patches to protocol

  buffers before/after a call gets submitted.

  """

  def __init__(self):

    """Constructor."""

    self.__content = []

    self.__unique_keys = set()

  def __len__(self):

    """Returns the amount of elements in the collection."""

    return self.__content.__len__()

  def __Insert(self, index, key, function, service=None):

    """Appends a hook at a certain position in the list.

    Args:

      index: the index of where to insert the function

      key: a unique key (within the module) for this particular function.

        If something from the same module with the same key is already

        registered, nothing will be added.

      function: the hook to be added.

      service: optional argument that restricts the hook to a particular api

    Returns:

      True if the collection was modified.

    """

    unique_key = (key, inspect.getmodule(function))

    if unique_key in self.__unique_keys:

      return False

    self.__content.insert(index, (key, function, service))

    self.__unique_keys.add(unique_key)

    return True

  def Append(self, key, function, service=None):

    """Appends a hook at the end of the list.

    Args:

      key: a unique key (within the module) for this particular function.

        If something from the same module with the same key is already

        registered, nothing will be added.

      function: the hook to be added.

      service: optional argument that restricts the hook to a particular api

    Returns:

      True if the collection was modified.

    """

    return self.__Insert(len(self), key, function, service)

  def Push(self, key, function, service=None):

    """Inserts a hook at the beginning of the list.

    Args:

      key: a unique key (within the module) for this particular function.

        If something from the same module with the same key is already

        registered, nothing will be added.

      function: the hook to be added.

      service: optional argument that restricts the hook to a particular api

    Returns:

      True if the collection was modified.

    """

    return self.__Insert(0, key, function, service)

  def Clear(self):

    """Removes all hooks from the list (useful for unit tests)."""

    self.__content = []

    self.__unique_keys = set()

  def Call(self, service, call, request, response):

    """Invokes all hooks in this collection.

    Args:

      service: string representing which service to call

      call: string representing which function to call

      request: protocol buffer for the request

      response: protocol buffer for the response

    """

    for key, function, srv in self.__content:

      if srv is None or srv == service:

        function(service, call, request, response)

    self.__precall_hooks = ListOfHooks()

    self.__postcall_hooks = ListOfHooks()

  def GetPreCallHooks(self):

    """Gets a collection for all precall hooks."""

    return self.__precall_hooks

  def GetPostCallHooks(self):

    """Gets a collection for all precall hooks."""

    return self.__postcall_hooks

  def MakeSyncCall(self, service, call, request, response):

    """The APIProxy entry point.

    Args:

      service: string representing which service to call

      call: string representing which function to call

      request: protocol buffer for the request

      response: protocol buffer for the response

    Raises:

      apiproxy_errors.Error or a subclass.

    """

    stub = self.GetStub(service)

    assert stub, 'No api proxy found for service "%s"' % service

    self.__precall_hooks.Call(service, call, request, response)

    stub.MakeSyncCall(service, call, request, response)

    self.__postcall_hooks.Call(service, call, request, response)