python学习笔记（七）之列表

列表：是一个加强版的数组，什么东西都可以往里面放。

创建列表

创建一个普通列表：

 >>> member = ['operating system', 'data structure', 'network', 'principle of computer composition']
 >>> member
 ['operating system', 'data structure', 'network', 'principle of computer composition']

创建一个混合列表：

 >>> mix = [1, 'hello python', 3.14159, [1,2,3,['one','two']]]
 >>> mix
 [1, 'hello python', 3.14159, [1, 2, 3, ['one', 'two']]]

创建一个空列表：

 >>> empty = []
 >>> empty
 []

向列表中添加元素

使用append()，extend(),和insert()方法

append()在尾部添加，extend()用一个列表来扩展列表，insert(index, obj)在index处插值。

 >>> member.append('mechine learning')
 >>> member
 ['operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning']
 >>> member.extend(['data mining', 'hadoop'])
 >>> member
 ['operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning', 'data mining', 'hadoop']
 >>> member.insert(0,'PE')
 >>> member
 ['PE', 'operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning', 'data mining', 'hadoop']

从列表中获取元素

和数组一样，通过元素的索引从列表中获得单个元素，索引从0开始。

 >>> for i in range(len(member)):
 ...     print(member[i])
 ...
 PE
 operating system
 data structure
 network
 principle of computer composition
 mechine learning
 data mining
 hadoop

通过列表分片

 >>> member[3]
 'network'
 >>> member[:3]
 ['PE', 'operating system', 'data structure']
 >>> member[3:]
 ['network', 'principle of computer composition', 'mechine learning', 'data mining', 'hadoop']
 >>> member[3:5]
 ['network', 'principle of computer composition']

从列表中删除元素

使用remove(),pop()方法或del

 >>> member
 ['PE', 'operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning', 'data mining', 'hadoop']
 >>> member.remove('hadoop')
 >>> member
 ['PE', 'operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning', 'data mining']
 >>> member.pop()
 'data mining'
 >>> member
 ['PE', 'operating system', 'data structure', 'network', 'principle of computer composition', 'mechine learning']
 >>> member.pop(2)
 'data structure'
 >>> member
 ['PE', 'operating system', 'network', 'principle of computer composition', 'mechine learning']
 >>> del member[3]
 >>> member
 ['PE', 'operating system', 'network', 'mechine learning']
 >>> del member
 >>> member
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
 NameError: name 'member' is not defined

列表的一些常用操作符

　　比较操作符 >， >=， < ，<=， == ，!=

 >>> list1 = [123]
 >>> list2 = [456]
 >>> list1 < list2
 True
 >>> list1 = [123,456]
 >>> list2 = [234,123]
 >>> list1 > list2
 False

　　逻辑操作符 and， or， not

 >>> list3 = [123,456]
 >>> list1 < list2 and list1 == list3
 True
 >>> list1 > list2 or list1 < list2
 True
 >>> not list1 < list2
 False

　　拼接操作符 *

 >>> list4 = list2 + list3
 >>> list4
 [234, 123, 123, 456]

　　重复操作符 *

 >>> list4
 [234, 123, 123, 456]
 >>> list4 * 5
 [234, 123, 123, 456, 234, 123, 123, 456, 234, 123, 123, 456, 234, 123, 123, 456, 234, 123, 123, 456]

　　成员关系操作符in， not in

 >>> 123 in list4
 True
 >>> 345 in list4
 False
 >>> 345 not in list4
 True

列表一些常用的方法

　　count():返回列表内某个成员出现次数，如果不存在则返回0

 >>> list4
 [234, 123, 123, 456]
 >>> list4.count(123)
 2

　　index()：返回该元素在列表第一次出现位置的索引，若不存在，则抛出一个ValueError异常。

 >>> list4.index(123)
 1
 >>> list4.index(124)
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
 ValueError: 124 is not in list

　　reverse():翻转列表

 >>> list4
 [456, 123, 123, 234]
 >>> list4.reverse()
 >>> list4
 [234, 123, 123, 456]