Python判断for循环最后一次的6种方法

在Python中，判断for循环是否是最后一次迭代可以通过多种方式实现。以下是6种常见的方法：

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方法1：使用enumerate和长度判断

通过enumerate获取索引，并结合序列长度判断是否为最后一次迭代。

items = [1, 2, 3, 4, 5]
for index, item in enumerate(items):
    if index == len(items) - 1:
        print(f"Last item: {item}")
    else:
        print(item)
items = [1, 2, 3, 4, 5]
for index, item in enumerate(items):
    if index == len(items) - 1:
        print(f"Last item: {item}")
    else:
        print(item)
items = [1, 2, 3, 4, 5]
for index, item in enumerate(items):
    if index == len(items) - 1:
        print(f"Last item: {item}")
    else:
        print(item)

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方法2：使用zip和itertools.islice

通过zip将当前元素与下一个元素配对，如果下一个元素不存在，则为最后一次迭代。

from itertools import islice
items = [1, 2, 3, 4, 5]
for current, next_item in zip(items, islice(items, 1, None)):
    print(current)
print(f"Last item: {items[-1]}")
from itertools import islice

items = [1, 2, 3, 4, 5]
for current, next_item in zip(items, islice(items, 1, None)):
    print(current)
print(f"Last item: {items[-1]}")
from itertools import islice

items = [1, 2, 3, 4, 5]
for current, next_item in zip(items, islice(items, 1, None)):
    print(current)
print(f"Last item: {items[-1]}")

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方法3：使用try-except捕获StopIteration

通过手动迭代器判断是否为最后一次迭代。

items = [1, 2, 3, 4, 5]
iterator = iter(items)
try:
    while True:
        item = next(iterator)
        try:
            next_item = next(iterator)
            print(item)
        except StopIteration:
            print(f"Last item: {item}")
            break
except StopIteration:
    pass
items = [1, 2, 3, 4, 5]
iterator = iter(items)
try:
    while True:
        item = next(iterator)
        try:
            next_item = next(iterator)
            print(item)
        except StopIteration:
            print(f"Last item: {item}")
            break
except StopIteration:
    pass
items = [1, 2, 3, 4, 5]
iterator = iter(items)
try:
    while True:
        item = next(iterator)
        try:
            next_item = next(iterator)
            print(item)
        except StopIteration:
            print(f"Last item: {item}")
            break
except StopIteration:
    pass

---

方法4：使用range和索引

通过range遍历索引，直接判断是否为最后一个索引。

items = [1, 2, 3, 4, 5]
for i in range(len(items)):
    if i == len(items) - 1:
        print(f"Last item: {items[i]}")
    else:
        print(items[i])
items = [1, 2, 3, 4, 5]
for i in range(len(items)):
    if i == len(items) - 1:
        print(f"Last item: {items[i]}")
    else:
        print(items[i])
items = [1, 2, 3, 4, 5]
for i in range(len(items)):
    if i == len(items) - 1:
        print(f"Last item: {items[i]}")
    else:
        print(items[i])

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方法5：使用itertools.pairwise（Python 3.10+）

在Python 3.10及以上版本中，可以使用itertools.pairwise来比较当前元素和下一个元素。

from itertools import pairwise
items = [1, 2, 3, 4, 5]
for current, next_item in pairwise(items + [None]):
    if next_item is None:
        print(f"Last item: {current}")
    else:
        print(current)
from itertools import pairwise

items = [1, 2, 3, 4, 5]
for current, next_item in pairwise(items + [None]):
    if next_item is None:
        print(f"Last item: {current}")
    else:
        print(current)
from itertools import pairwise

items = [1, 2, 3, 4, 5]
for current, next_item in pairwise(items + [None]):
    if next_item is None:
        print(f"Last item: {current}")
    else:
        print(current)

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方法6：使用标志变量

通过设置一个标志变量来判断是否为最后一次迭代。

items = [1, 2, 3, 4, 5]
last_index = len(items) - 1
for index, item in enumerate(items):
    if index == last_index:
        print(f"Last item: {item}")
    else:
        print(item)
items = [1, 2, 3, 4, 5]
last_index = len(items) - 1
for index, item in enumerate(items):
    if index == last_index:
        print(f"Last item: {item}")
    else:
        print(item)
items = [1, 2, 3, 4, 5]
last_index = len(items) - 1
for index, item in enumerate(items):
    if index == last_index:
        print(f"Last item: {item}")
    else:
        print(item)

---

总结

方法	优点	缺点
enumerate + 长度判断	简单直观	需要额外计算长度
zip + itertools.islice	避免计算长度	需要额外导入itertools
try-except + StopIteration	适用于手动控制迭代器	代码稍显复杂
range + 索引	直接通过索引判断	需要额外计算长度
itertools.pairwise	简洁（Python 3.10+）	仅适用于Python 3.10及以上版本
标志变量	简单易用	需要额外变量

根据具体场景选择合适的方法即可！