python中有帮助函数吗

>>>import struct
>>>dir() # show the names in the module namespace
['__builtins__','__doc__','__name__','struct']
>>>dir(struct) # show the names in the struct module
['Struct','__builtins__','__doc__','__file__','__name__',
 '__package__','_clearcache','calcsize','error','pack','pack_into',
 'unpack','unpack_from']
>>>class Shape(object):
    def __dir__(self):
      return ['area','perimeter','location']
>>> s= Shape()
>>>dir(s)

['area', 'perimeter', 'location']
Note Because dir() is supplied primarily as a convenience for use at an interactive prompt, it tries 
to supply an 
interesting set of names more than it tries to supply a rigorously or consistently defined set of 
names, and its 
detailed behavior may change across releases. For example, metaclass attributes are not in the result 
list when the 
argument is a class.

>>>dir()
['__builtins__','__doc__','__name__','__package__']
>>>import struct
>>>dir()
['__builtins__','__doc__','__name__','__package__','struct']
>>>dir(struct)
['Struct','__builtins__','__doc__','__file__','__name__','__package__','_clearcache','calcsize','error','pack',
'pack_into','unpack','unpack_from']
>>>class Person(object):
...  def __dir__(self):
...      return ["name","age","country"]
...
>>>dir(Person)
['__class__','__delattr__','__dict__','__dir__','__doc__','__format__','__getattribute__','__hash__','__init__',
'__module__','__new__','__reduce__','__reduce_ex__','__repr__','__setattr__','__sizeof__','__str__','__subclasshook__',
'__weakref__']
>>> tom= Person()
>>>dir(tom)
['age','country','name']

>>> help('dir')
Help on built-in function dir in module builtins:
dir(...)
  dir([object]) -> list of strings

  If called without an argument, return the names in the current scope.
  Else, return an alphabetized list of names comprising (some of) the attribut
es
  of the given object, and of attributes reachable from it.
  If the object supplies a method named __dir__, it will be used; otherwise
  the default dir() logic is used and returns:
   for a module object: the module's attributes.
   for a class object: its attributes, and recursively the attributes
    of its bases.
   for any other object: its attributes, its class's attributes, and
    recursively the attributes of its class's base classes.