def list_operations(self, name, filter_, page_size=0, options=None):
        """
        Lists operations that match the specified filter in the request. If the
        server doesn't support this method, it returns ``UNIMPLEMENTED``.
        NOTE: the ``name`` binding below allows API services to override the binding
        to use different resource name schemes, such as ``users/*/operations``.

        Example:
          >>> from google.gapic.longrunning import operations_client
          >>> from google.gax import CallOptions, INITIAL_PAGE
          >>> api = operations_client.OperationsClient()
          >>> name = ''
          >>> filter_ = ''
          >>>
          >>> # Iterate over all results
          >>> for element in api.list_operations(name, filter_):
          >>>   # process element
          >>>   pass
          >>>
          >>> # Or iterate over results one page at a time
          >>> for page in api.list_operations(name, filter_, options=CallOptions(page_token=INITIAL_PAGE)):
          >>>   for element in page:
          >>>     # process element
          >>>     pass

        Args:
          name (string): The name of the operation collection.
          filter_ (string): The standard list filter.
          page_size (int): The maximum number of resources contained in the
            underlying API response. If page streaming is performed per-
            resource, this parameter does not affect the return value. If page
            streaming is performed per-page, this determines the maximum number
            of resources in a page.
          options (:class:`google.gax.CallOptions`): Overrides the default
            settings for this call, e.g, timeout, retries etc.

        Returns:
          A :class:`google.gax.PageIterator` instance. By default, this
          is an iterable of :class:`google.longrunning.operations_pb2.Operation` instances.
          This object can also be configured to iterate over the pages
          of the response through the `CallOptions` parameter.

        Raises:
          :exc:`google.gax.errors.GaxError` if the RPC is aborted.
          :exc:`ValueError` if the parameters are invalid.
        """
        # Create the request object.
        request = operations_pb2.ListOperationsRequest(
            name=name, filter=filter_, page_size=page_size)
        return self._list_operations(request, options)