這將循環遍歷列表，並且列表中的每個元素在每次迭代中都可以作為變數使用。當需要遍歷清單中的所有元素時，這被廣泛使用。
operating_systems = ["windows", "mac", "linux"]
for os in operating_systems:
print(os)`
# Output windows mac linux
當需要根據索引存取並且需要索引值時。
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
如果您同時需要索引和值，這是一種優雅的方式
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
可以很好地控制何時向前移動迭代器，儘管我們必須依靠 StopIteration 來檢查是否到達末端。
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
需要轉換時
operating_systems = ["windows", "mac", "linux"] os_uppercase = [os.upper() for os in operating_systems] print(os_uppercase)
# Output ['WINDOWS', 'MAC', 'LINUX']
當需要循環列表時。使用適當的邊界條件來打破循環
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
同時循環多個列表。如果清單大小不同，請注意輸出。
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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