Python序列——列表

1. 列表是什么

列表也是序列的一种。列表能保存任意数目的Python对象，列表是可变类型。

1.1 创建列表

列表可以使用[]来创建，或者使用工厂方法list()来创建。

>>> t = list()
>>> type(t)
<type ‘list‘>
>>> l = []
>>> type(l)
<type ‘list‘>
>>> t == l
True

1.2 访问列表和更新列表

>>> t = list(‘furzoom‘)
>>> t
[‘f‘, ‘u‘, ‘r‘, ‘z‘, ‘o‘, ‘o‘, ‘m‘]
>>> t[1]
‘u‘
>>> t[2] = ‘n‘
>>> t
[‘f‘, ‘u‘, ‘n‘, ‘z‘, ‘o‘, ‘o‘, ‘m‘]
>>> t.append(‘.‘)
>>> t
[‘f‘, ‘u‘, ‘n‘, ‘z‘, ‘o‘, ‘o‘, ‘m‘, ‘.‘]
>>> del t[3]
>>> t
[‘f‘, ‘u‘, ‘n‘, ‘o‘, ‘o‘, ‘m‘, ‘.‘]
>>> del t
>>> t
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name ‘t‘ is not defined

2. 列表相关操作

支持比较运算、切片[]或者[:]、in, not in、连接操作符+、重复操作。

如果可以，尽量使用list.extend()方式代替连接操作符。

列表还支持非常重要的列表解析操作。

>>> [i for i in xrange(10)]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

3. 内建函数对列表的支持

3.1 cmp()

比较原则：

1. 对两个列表的元素进行比较。
2. 如果比较的元素是同类型的，则比较其值，返回结果。
3. 如果两个元素不是同一类型的，则检查它们是否是数字。
   3.1 如果是数字，执行必要的数字强制类型转换，然后比较。
   3.2 如果有一方的元素是数字，则另一方的元素大。
   3.3 否则，通过类型名字的字母顺序进行比较。
4. 如果有一个列表首先到达末尾，则另一个长一点的列表大。
5. 如果两个列表都到达结尾，且所有元素都相等，则返回0。

3.2 序列类型函数

• len()
• max()
• min()
• sorted()
• reversed()
• enumerate()
• zip()
• sum()
• list()
• tuple()

4. 列表内建函数

• list.append(x)
• list.extend(x)
• list.count(x)
• list.index(x[, start[, end]])
• list.insert(index, x)
• list.pop([index])
• list.remove(x)
• list.remove()
• list.sort([cmp[, key[, reverse]]])

5. 列表应用

5.1 堆栈

#!/usr/bin/env python
# -*- coding: utf-8 -*-

stack = []


def pushit():
    stack.append(raw_input(‘Enter New string: ‘).strip())


def popit():
    if len(stack) == 0:
        print ‘Cannot pop from an empty stack!‘
    else:
        print ‘Removed [‘, `stack.pop()`, ‘]‘


def viewstack():
    print stack


CMDs = {‘u‘: pushit, ‘o‘: popit, ‘v‘: viewstack}


def showmenu():
    pr = """
    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: """
    while True:
        while True:
            try:
                choice = raw_input(pr).strip()[0].lower()
            except (EOFError, KeyboardInterrupt, IndexError):
                choice = ‘q‘

            print ‘\nYou picked: [%s]‘ % choice
            if choice not in ‘uovq‘:
                print ‘Invalid option, try again‘
            else:
                break

        if choice == ‘q‘:
            break

        CMDs[choice]()


if __name__ == ‘__main__‘:
    showmenu()

运行示例如下：

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: u

You picked: [u]
Enter New string: Python

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: u

You picked: [u]
Enter New string: is

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: u

You picked: [u]
Enter New string: cool!

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: v

You picked: [v]
[‘Python‘, ‘is‘, ‘cool!‘]

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: o

You picked: [o]
Removed [ ‘cool!‘ ]

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: o

You picked: [o]
Removed [ ‘is‘ ]

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: o

You picked: [o]
Removed [ ‘Python‘ ]

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: o

You picked: [o]
Cannot pop from an empty stack!

    p(U)sh
    p(O)p
    (V)iew
    (Q)uit

    Enter choice: ^D

You picked: [q]

5.2 队列

#!/usr/bin/env python
# -*- coding: utf-8 -*-

queue = []


def enQ():
    queue.append(raw_input(‘Enter New string: ‘).strip())


def deQ():
    if len(queue) == 0:
        print ‘Cannot pop from an empty queue!‘
    else:
        print ‘Removed [‘, `queue.pop(0)`, ‘]‘


def viewQ():
    print queue


CMDs = {‘e‘: enQ, ‘d‘: deQ, ‘v‘: viewQ}


def showmenu():
    pr = """
    (E)nqueue
    (D)equeue
    (V)iew
    (Q)uit

    Enter choice: """
    while True:
        while True:
            try:
                choice = raw_input(pr).strip()[0].lower()
            except (EOFError, KeyboardInterrupt, IndexError):
                choice = ‘q‘

            print ‘\nYou picked: [%s]‘ % choice
            if choice not in ‘edvq‘:
                print ‘Invalid option, try again‘
            else:
                break

        if choice == ‘q‘:
            break

        CMDs[choice]()


if __name__ == ‘__main__‘:
    showmenu()

运行示例如下：

    (E)nqueue
    (D)equeue
    (V)iew
    (Q)uit

    Enter choice: e

You picked: [e]
Enter New string: Bring out

    (E)nqueue
    (D)equeue
    (V)iew
    (Q)uit

    Enter choice: e

You picked: [e]
Enter New string: your dead!

    (E)nqueue
    (D)equeue
    (V)iew
    (Q)uit

    Enter choice: v

You picked: [v]
[‘Bring out‘, ‘your dead!‘]

    (E)nqueue
    (D)equeue
    (V)iew
    (Q)uit

    Enter choice: d

You picked: [d]
Removed [ ‘Bring out‘ ]

    (E)nqueue
    (D)equeue
    (V)iew
    (Q)uit

    Enter choice: d

You picked: [d]
Removed [ ‘your dead!‘ ]

    (E)nqueue
    (D)equeue
    (V)iew
    (Q)uit

    Enter choice: d

You picked: [d]
Cannot pop from an empty queue!

    (E)nqueue
    (D)equeue
    (V)iew
    (Q)uit

    Enter choice: ^D

You picked: [q]