第四章 操作列表与for循环

4.1 for循环语句

# encoding=utf-8
magicians = ['jun', 'bin', 'qi', 'feng']
for magician in magicians:
    print('welcome ' + magician.title())
    print(magician + ",that was a great trick")
# 虽然不推荐，但人家确实活着
print("game end")
print("变量仍然活着:" + magician)

welcome Jun
jun,that was a great trick
welcome Bin
bin,that was a great trick
welcome Qi
qi,that was a great trick
welcome Feng
feng,that was a great trick
game end
变量仍然活着:feng

4.2关于python的缩进认知：

Python根据缩进判断代码行之间的关系.这点与java完全不同
在代码行for magician in magicians:后面，每个缩进的代码行都是循环的一部分.而不属于循环部分的代码请不要缩进.

不必要的缩进错误

4.3创建数值列表

range()函数可以生成一系列数字，也可以调整步长，左闭右开
list()函数
max()
min()
sum()

# encoding=utf-8
# 左闭右开
for value in range(1, 5):
    print(value)
# 可以指定步长
for value in range(2, 20, 2):
    print(value)
numbers = range(1, 10)
print(numbers)
print(list(numbers))

suquares = []
suquares = list()
for value in range(1, 11):
    suquares.append(value ** 2)
print(suquares)

digits = [1, 2, 3, 4, 5, 6]
print(min(digits))
print(max(digits))
print(sum(digits))
print(min(1, 3, 5, 6))

# 列表解析:一行代码生成平方数列表
suquares = [value ** 2 for value in range(1, 11)]
print(suquares)

1
2
3
4
2
4
6
8
10
12
14
16
18
range(1, 10)
[1, 2, 3, 4, 5, 6, 7, 8, 9]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
1
6
21
1
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

4.4.1切片

创建切片，可指定要使用的第一个元素和最后一个元素的索引。左闭右开。

切片是列表的副本,不修改原始列表。
复制整个列表

>>>players[:]

# encoding=utf-8
players = ['zhang san', 'li si ', 'wang wu', 'zhao liu']
# 获取前两名队员
print(players[0:2])
# 默认从开头开始
print(players[:3])
# 默认到结尾结束
print(players[2:])
print(players[:-1])
print('last 3 players:' + str(players[-3:]))

# 遍历切片
for player in players[:3]:
    print(player)

# 利用列表切片复制整个列表
my_players = players[:]
my_players.append("qian qi")
print('---------=====--------')
for my_player in my_players:
    print(my_player)
print('---------=====--------')
for player in players:
    print(player)

['zhang san', 'li si ']
['zhang san', 'li si ', 'wang wu']
['wang wu', 'zhao liu']
['zhang san', 'li si ', 'wang wu']
last 3 players:['li si ', 'wang wu', 'zhao liu']
zhang san
li si 
wang wu
---------=====--------
zhang san
li si 
wang wu
zhao liu
qian qi
---------=====--------
zhang san
li si 
wang wu
zhao liu

4.5元组

python把不能修改的值成为不可变的，而不可变的列表成为元组。
不能修改元组里的元素，但可以给元组变量重新赋值一个新的元组

# encoding=utf-8
# 元组
dimensions = (80, 200, 500)
print(dimensions)
print(dimensions[0])
print(dimensions[1])

# TypeError: 'tuple' object does not support item assignment
# dimensions[0] = 40

# 修改元组变量，可以给整个变量重新赋值
dimensions = (800, 200, 500, 600)
print(dimensions)

(80, 200, 500)
80
200
(800, 200, 500, 600)

4.6

PEP8(Python Enhancement Proposal) Python改进提案，为python程序员提供了代码格式设置指南。