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)`
# outputwindowsmaclinux
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]}")
# outputindex 0: windowsindex 1: macindex 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}")
# outputindex is 0 and value is windowsindex is 1 and value is macindex is 2 and value is linux
尽管
简单的同时
operating_systems = ["windows", "mac", "linux"]i = 0 # inital condition, required to startwhile 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
# outputwhile looping 0 got the value windowswhile looping 1 got the value macwhile 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
# outputconsumed form iterator windowsconsumed form iterator macconsumed form iterator linuxconsumed all from iterator
# hack to avoid stopiterationiterator = iter(operating_systems)end_of_list = object()reached_end = falsewhile 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 itertoolsoperating_systems = ["windows", "mac", "linux"]for item in itertools.cycle(operating_systems): print(item)# infinite cycling loopmake sure to have proper boundary condition to break
# outputwindowsmaclinuxwindowsmaclinuxwindowsmaclinuxwindowsmaclinuxwindows ....... 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)
# outputwindows androidmac ios
反向循环
operating_systems = ["windows", "mac", "linux"]for reversed_os in reversed(operating_systems): print(reversed_os)
# Outputlinuxmacwindows
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