python入门必会的助手函数：dir()函数

dir([object])

Without arguments, return the list of names in the current local scope. With an argument, attempt to return a list of

 valid attributes for that object.

If the object has a method named __dir__(), this method will be called and must return the list of attributes. This

 allows objects that implement a custom __getattr__() or __getattribute__() function to customize the way dir()

  reports their attributes.

If the object does not provide __dir__(), the function tries its best to gather information from the object’

s __dict__ attribute, if defined, and from its type object. The resulting list is not necessarily complete, and may be

 inaccurate when the object has a custom __getattr__().

The default dir() mechanism behaves differently with different types of objects, as it attempts to produce the most

relevant, rather than complete, information:

If the object is a module object, the list contains the names of the module’s attributes.

If the object is a type or class object, the list contains the names of its attributes, and recursively of the

attributes of its bases.

Otherwise, the list contains the object’s attributes’ names, the names of its class’s attributes, and recursively

 of the attributes of its class’s base classes.

>>>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']