dir:可以用来查看模块中的所有特性（函数，类，变量等）
>>> import copy >>> dir(copy) ['Error', 'PyStringMap', '_EmptyClass', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', '_c opy_dispatch', '_copy_immutable', '_copy_with_constructor', '_copy_with_copy_met hod', '_deepcopy_atomic', '_deepcopy_dict', '_deepcopy_dispatch', '_deepcopy_lis t', '_deepcopy_method', '_deepcopy_tuple', '_keep_alive', '_reconstruct', 'built ins', 'copy', 'deepcopy', 'dispatch_table', 'error', 'name', 't', 'weakref'] >>> [x for x in dir(copy) if not x.startswith('_')] ['Error', 'PyStringMap', 'builtins', 'copy', 'deepcopy', 'dispatch_table', 'erro r', 'name', 't', 'weakref']