Chapter 04:列表操作

for循环依次遍历

PS:使用单数和复数式名称，可帮助你判断代码段处理的是单个列表元素还是整个列表

magicians = ['alice', 'david', 'carolina']
for magican in magicians:
    print(magican)

alice
david
carolina

c风格for循环也可以

for i in range(len(magicians)):
    print(magicians[i])

alice
david
carolina

函数range()可上传一系列数字，不制定首元素，默认从0开始

print(range(5))

range(0, 5)

range() 可转化为列表

PS:生成的列表元素为range的前闭后开区间，这与其他语言保持一致

numbers = list(range(1,6))
print(numbers)

[1, 2, 3, 4, 5]

range接受第三个参数，表示步长，此时必须指明起始位置

even_numbers = list(range(2,15,2))
print(even_numbers)

[2, 4, 6, 8, 10, 12, 14]

步长可以是复数，但记得这样做要保证起始位置大于末尾位置

odd_numbers = list(range(50,29,-3))
print(odd_numbers)

[50, 47, 44, 41, 38, 35, 32]

数值列表简单统计

print(max(even_numbers), min(numbers), sum(even_numbers))

14 1 56

列表解析创建列表

squares = [value ** 2 for value in range(1,11)]
print(squares)

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

计算1到1000000的累加和

sum([value for value in range(1,1000001)])

500000500000

可以用冒号（:）来进行“切片”操作

players = ['charles', 'martina', 'michael', 'florence', 'eli']
print(players[0:3])
print(players[:4])
print(players[1:4])
print(players[2:])
print(players[-2:])
print(players[::-2])

['charles', 'martina', 'michael']
['charles', 'martina', 'michael', 'florence']
['martina', 'michael', 'florence']
['michael', 'florence', 'eli']
['florence', 'eli']
['eli', 'michael', 'charles']

列表的复制

my_foods = ['pizza', 'falafel', 'carrot cake']
friend_foods = my_foods[:]
print(my_foods)
print(friend_foods)
my_foods.append("canoli")
friend_foods.append("ice cream")
print(my_foods)
print(friend_foods)

['pizza', 'falafel', 'carrot cake']
['pizza', 'falafel', 'carrot cake']
['pizza', 'falafel', 'carrot cake', 'canoli']
['pizza', 'falafel', 'carrot cake', 'ice cream']

徜若直接用等号（=）进行列表拷贝，将不能得到一个新的列表，这是因为列表名仅是一个指向列表的指针

类比C的指针赋值，浅拷贝与深拷贝

self_foods = my_foods
my_foods.append('ice cream')
print(my_foods)
print(self_foods)

['pizza', 'falafel', 'carrot cake', 'canoli', 'ice cream']
['pizza', 'falafel', 'carrot cake', 'canoli', 'ice cream']

圆括号() 可创建元组，元组是不可改边的列表

dimensions = (200,50)
print(dimensions[0],dimensions[1])

200 50

元组内容不可修改，但是元素本身却可以多次赋值

dimensions = (400,20)
print(dimensions[0],dimensions[1])

400 20