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
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
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
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
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
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']
当需要循环列表时。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
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
operating_systems = ["windows", "mac", "linux"]
for reversed_os in reversed(operating_systems):
print(reversed_os)
# Output linux mac windows
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