Python List和Tuple的区别

  面试中老是会问这个，还问使用场景，不过我一般只用list很少使用tuple，
没读过源码，简单的可以从以下几个方面说:

  1.列表里的内容是可以改变的，增删改都可以，tuple则不行:

>>> alist = [1,2,3,4]
>>> atuple = (1,2,3,4)
>>> atuple.append(1)
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: 'tuple' object has no attribute 'append'
>>> dir(atuple)
['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'count', 'index']
>>> dir(alist)
['__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']

可以看出tuple根本没有修改的方法.

2.在Python中，字典的key必须是可哈希的，不可变的，所以tuple可以作为字典的键，而list则不行:

>>> adict = {}
>>> atuple = (1,2,3)
>>> adict[atuple] = 'ok'
>>> adict
{(1, 2, 3): 'ok'}
>>> alist = [1,2,3]
>>> adict[alist] = 'not ok'
Traceback (most recent call last):
  File "", line 1, in 
TypeError: unhashable type: 'list'

3.对于使用场景，tuple适合一些只读数据，如Python连接MySQL得到的结果就是使用tuple，
而list则在列表长度不固定或者需要有变动的数据中使用，另外，tuple的性能要比list好一些，
tuple比list更省内存:

>>> a = list(xrange(100000))
>>> a.__sizeof__()
900088
>>> b = tuple(xrange(100000))
>>> b.__sizeof__()
800024

而且更快,具体测试方法，参考stackoverflow