dir和help是Python中两个强大的built-in函数，就像Linux的man一样，绝对是开发的好帮手。比如查看list的所以属性:
dir(list)
输出：
['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__delslice__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getslice__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__setslice__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']
然后查看list的pop方法的作用和用法：
help(list.pop)
输出：
Help on method_descriptor:
pop(...)
L.pop([index]) -> item -- remove and return item at index (default last).
Raises IndexError if list is empty or index is out of range.
(END)
