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python函数每日一讲 - dir()

最近确实是有些忙,刚过了年,积累了许多工作需求处理,所以每日一函数只能是每两天更新一篇,在这里和咱们致歉。

今日咱们来看一个非常重要的函数:dir()

中文阐明:不带参数时,回来当时范围内的变量、办法和界说的类型列表;带参数时,回来参数的特点、办法列表。假如参数包括办法__dir__(),该办法将被调用。假如参数不包括__dir__(),该办法将最大极限地搜集参数信息。

参数object: 目标、变量、类型。

版别:该函数在python各个版别中都有,可是每个版别中显现的特点细节有所不同。使用时留意差异。

英文阐明

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.

The resulting list is sorted alphabetically. For example:

>>> 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.


特别阐明:改系列文章一切代码实例没有特别阐明则都是根据python2.7

代码实例:

>>> 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']


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