python中有帮助函数吗

时间:2020-06-19 silencement 人气:3

python中的dir()函数是一个非常重要的函数，它可以帮助我们查看函数的功能和特性。

中文说明：不带参数时，返回当前范围内的变量、方法和定义的类型列表；带参数时，返回参数的属性、方法列表。如果参数包含方法__dir__()，该方法将被调用。如果参数不包含__dir__()，该方法将最大限度地收集参数信息。

参数object：对象、变量、类型。

版本：该函数在python各个版本中都有，但是每个版本中显示的属性细节有所不同。使用时注意区别。

例如

>>>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.

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']

知识点扩展：

help()函数的作用

在使用python来编写代码时，会经常使用python自带函数或模块，一些不常用的函数或是模块的用途不是很清楚，这时候就需要用到help函数来查看帮助。

这里要注意下，help()函数是查看函数或模块用途的详细说明，而dir()函数是查看函数或模块内的操作方法都有什么，输出的是方法列表。

怎么使用help函数查看python模块中函数的用法

help()括号内填写参数，操作方法很简单。例如：

>>> 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.

加载全部内容