掌握 Python 列表：您需要了解的基本技术

为了

简单的

这将循环遍历列表，并且列表中的每个元素在每次迭代中都可以作为变量使用。当需要遍历列表中的所有元素时，这被广泛使用。

operating_systems = ["windows", "mac", "linux"]
for os in operating_systems:
    print(os)`

# output
windows
mac
linux

对于和范围

当需要根据索引访问并且需要索引值时。

operating_systems = ["windows", "mac", "linux"]
for i in range(len(operating_systems)):
    print(f"index {i}: {operating_systems[i]}")

# output
index 0: windows
index 1: mac
index 2: linux

为并枚举

如果您同时需要索引和值，这是一种优雅的方式

operating_systems = ["windows", "mac", "linux"]
for index, os in enumerate(operating_systems):
    print(f"index is {index} and value is {os}")

# output
index is 0 and value is windows
index is 1 and value is mac
index is 2 and value is linux

尽管

简单的同时

operating_systems = ["windows", "mac", "linux"]
i = 0 # inital condition, required to start
while i < len(operating_systems):
    print(f"while looping {i} got the value {operating_systems[i]}")
    i = i + 1 # this is very important, dont forget about infinite loops

# output
while looping 0 got the value windows
while looping 1 got the value mac
while looping 2 got the value linux

迭代器

可以很好地控制何时向前移动迭代器，尽管我们必须依靠 stopiteration 来检查是否到达末尾。

operating_systems = ["windows", "mac", "linux"]
iterator = iter(operating_systems)
while true:
    try:
        os = next(iterator)
        print(f"consumed form iterator {os}")
    except stopiteration:
        print("consumed all from iterator")
        break

# output
consumed form iterator windows
consumed form iterator mac
consumed form iterator linux
consumed all from iterator

# hack to avoid stopiteration
iterator = iter(operating_systems)
end_of_list = object()
reached_end = false
while not reached_end:
    os = next(iterator, end_of_list)# a predefined object as end of the list
    if os != end_of_list:
        print(os)
    else:
        reached_end = true

列表理解

需要转型时

operating_systems = ["windows", "mac", "linux"]
os_uppercase = [os.upper() for os in operating_systems]
print(os_uppercase) 

# output
['windows', 'mac', 'linux']

骑自行车

当需要循环浏览列表时。使用适当的边界条件来打破循环

import itertools
operating_systems = ["windows", "mac", "linux"]
for item in itertools.cycle(operating_systems):  
    print(item)
# infinite cycling loopmake sure to have proper boundary condition to break

# output
windows
mac
linux
windows
mac
linux
windows
mac
linux
windows
mac
linux
windows ....... infinite loop

多个列表

同时循环多个列表。如果列表大小不同，请注意输出。

operating_systems = ["windows", "mac", "linux"]
mobile_operating_systems = ["android", "ios"]

for os, mobile_os in zip(operating_systems,mobile_operating_systems):
    print(os, mobile_os)

# output
windows android
mac ios

反向循环

operating_systems = ["windows", "mac", "linux"]
for reversed_os in reversed(operating_systems):
    print(reversed_os)

# Output
linux
mac
windows

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