tensorflow学习笔记（四十五）：sess.run(tf.global_variables_initializer()) 做了什么？

def global_variables_initializer():
  """Returns an Op that initializes global variables.
  Returns:
    An Op that initializes global variables in the graph.
  """
  return variables_initializer(global_variables())

def global_variables():
  """Returns global variables.
  Returns:
    A list of `Variable` objects.
  """
  return ops.get_collection(ops.GraphKeys.GLOBAL_VARIABLES)

def variables_initializer(var_list, name="init"):
  """Returns an Op that initializes a list of variables.
  Args:
    var_list: List of `Variable` objects to initialize.
    name: Optional name for the returned operation.

  Returns:
    An Op that run the initializers of all the specified variables.
  """
  if var_list:
    return control_flow_ops.group(*[v.initializer for v in var_list], name=name)
  return control_flow_ops.no_op(name=name)

class Variable(object):
    def _init_from_args(self, ...):
        self._initializer_op = state_ops.assign(
            self._variable, self._initial_value,
            validate_shape=validate_shape).op
    @property
    def initializer(self):
        """The initializer operation for this variable."""
        return self._initializer_op