py3学习笔记3(列表)

  Python可以分辨一堆不同的复合数据类型,并可以将他们整合在一起。列表(list)就是一种非常出色的方法。它可以用方括号将将一堆以逗号分隔的项整合在一起。可以包含不同的数据类型,但日常使用时常用相同的数据类型。

>>> squares = [1, 4, 9, 16, 25]
>>> squares
[1, 4, 9, 16, 25]

   跟所有的内置序列类型一样(built-in sequence type),对list可以执行索引(index)和切片(slice)操作

>>> squares[0] # indexing returns the item
1
>>> squares[-1]
25
>>> squares[-3:] # slicing returns a new list
[9, 16, 25]

  所有的slice操作都将返回一个操作后的新list。list也支持像串接( concatenation)的操作

>>> squares + [36, 49, 64, 81, 100]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

  list不像string,它是可变的(mutable),可以改变其中的内容

>>> cubes = [1, 8, 27, 65, 125] # something's wrong here
>>> 4**3 # the cube of 4 is 64, not 65!
64
>>> cubes[3] = 64 # replace the wrong value
>>> cubes
[1, 8, 27, 64, 125]

  你也可以使用append()方法在list的末尾添加新的项

>>> cubes.append(216) # add the cube of 6
>>> cubes.append(7**3) # and the cube of 7
>>> cubes
[1, 8, 27, 64, 125, 216, 343]

  使用slice方法对list进行操作时,可以改变list的大小甚至清空

>>> letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> letters
['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> # replace some values
>>> letters[2:5] = ['C', 'D', 'E']
>>> letters
['a', 'b', 'C', 'D', 'E', 'f', 'g']
>>> # now remove them
>>> letters[2:5] = []
>>> letters
['a', 'b', 'f', 'g']
>>> # clear the list by replacing all the elements with an empty list
>>> letters[:] = []
>>> letters
[]

  内置函数len()也同样适用于list

>>> letters = ['a', 'b', 'c', 'd']
>>> len(letters)
4

  将list作为项整合为list也是可行的

>>> a = ['a', 'b', 'c']
>>> n = [1, 2, 3]
>>> x = [a, n]
>>> x
[['a', 'b', 'c'], [1, 2, 3]]
>>> x[0]
['a', 'b', 'c']
>>> x[0][1]
'b'
原文地址:https://www.cnblogs.com/jzl123/p/5864375.html