python help函数

help()函数是python的一个内置函数

注意： python的内置函数可以直接调用，不需要import导入，它是python自带的函数，任何时候都可以被使用。

一、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。
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。

二、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.

三、使用help函数查看帮助实例

在写help()函数使用方法时说过，括号中填写参数，那在这里要注意参数的形式：

1、查看一个模块的帮助

>>>help('sys')
<pre style="box-sizing: border-box; font-family: Consolas; overflow: auto; font-size: 12pt; display: block; padding: 1px 0px; margin: 0px; line-height: inherit; color: rgb(0, 0, 0); word-break: break-all; overflow-wrap: break-word; background-color: rgb(255, 255, 255); border: 0px; border-radius: 0px; white-space: pre-wrap; vertical-align: baseline; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">Help on built-in module sys:

NAME
    sys

MODULE REFERENCE
    [https://docs.python.org/3.7/library/sys](https://docs.python.org/3.7/library/sys)

    The following documentation is automatically generated from the Python
    source files.  It may be incomplete, incorrect or include features that
    are considered implementation detail and may vary between Python
    implementations.  When in doubt, consult the module reference at the
    location listed above.

DESCRIPTION
    This module provides access to some objects used or maintained by the
    interpreter and to functions that interact strongly with the interpreter.</pre>

它会打开这个模块的帮助文档。

2、查看一个数据类型的帮助

返回字符串的方法及详细说明:

>>>help('str')
>>>a = [1,2,3]
>>>help(a)
 self+=value.
 |  
 |  __imul__(self, value, /)
 |      Implement self*=value.
 |  
 |  __init__(self, /, *args, **kwargs)
 |      Initialize self.  See help(type(self)) for accurate signature.
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __mul__(self, value, /)
 |      Return self*value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __reversed__(self, /)
 |      Return a reverse iterator over the list.
 |  
 |  __rmul__(self, value, /)
 |      Return value*self.
 |  
 |  __setitem__(self, key, value, /)
 |      Set self[key] to value.
 |  
 |  __sizeof__(self, /)
 |      Return the size of the list in memory, in bytes.
 |  
 |  append(self, object, /)
 |      Append object to the end of the list.
 |  
 |  clear(self, /)
 |      Remove all items from list.
 |  
 |  copy(self, /)
 |      Return a shallow copy of the list.
 |  
 |  count(self, value, /)
 |      Return number of occurrences of value.
 |  
 |  extend(self, iterable, /)
 |      Extend list by appending elements from the iterable.
 |  
 |  index(self, value, start=0, stop=9223372036854775807, /)
 |      Return first index of value.
 |      
 |      Raises ValueError if the value is not present.
 |  
 |  insert(self, index, object, /)
 |      Insert object before index.
 |  
 |  pop(self, index=-1, /)
 |      Remove and return item at index (default last).
 |      
 |      Raises IndexError if list is empty or index is out of range.
 |  
 |  remove(self, value, /)
 |      Remove first occurrence of value.
 |      
 |      Raises ValueError if the value is not present.
 |  
 |  reverse(self, /)
 |      Reverse *IN PLACE*.
 |  
 |  sort(self, /, *, key=None, reverse=False)
 |      Stable sort *IN PLACE*.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __hash__ = None

这时help(a)则会打开list的操作方法。

查看list的append方法的帮助

>>>help(a.append)
Help on built-in function append:

append(object, /) method of builtins.list instance
    Append object to the end of the list.