python function - dir()

I have been really busy recently. The New Year has just passed and I have accumulated a lot of things that need to be dealt with, so I can only update one post every two days. I would like to apologize to everyone here.

Today we take a look at a very important function: dir()

Chinese description: without parameters, returns a list of variables, methods and defined types in the current scope; with parameters, returns a list of attributes and methods of the parameters . If the argument contains the method __dir__(), this method will be called. If the parameter does not contain __dir__(), this method will collect parameter information to the maximum extent possible.

Parameter object: object, variable, type.

Version: This function is available in various versions of python, but the attribute details displayed in each version are different. Pay attention to the difference when using it.

English description:

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. ', '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.

Special Note: All code examples in this series of articles will be changed without special instructions Is based on python2.7

Code 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)

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