精通 Python 循环控制：20 个提高编程效率的高级技巧

# 示例：遍历列表
fruits = ['apple', 'banana', 'cherry']
for fruit in fruits:
    print(fruit)

apple
banana
cherry

# 示例：使用 enumerate 获取索引和值
fruits = ['apple', 'banana', 'cherry']
for index, fruit in enumerate(fruits):
    print(f"Index: {index}, Fruit: {fruit}")

Index: 0, Fruit: apple
Index: 1, Fruit: banana
Index: 2, Fruit: cherry

# 示例：使用 range 生成数字序列
for i in range(5):
    print(i)

0
1
2
3
4

# 示例：使用 zip 同时遍历多个列表
names = ['Alice', 'Bob', 'Charlie']
ages = [25, 30, 35]
for name, age in zip(names, ages):
    print(f"{name} is {age} years old")

Alice is 25 years old
Bob is 30 years old
Charlie is 35 years old

# 示例：使用 break 提前终止循环
for i in range(10):
    if i == 5:
        break
    print(i)

0
1
2
3
4

# 示例：使用 continue 跳过当前迭代
for i in range(10):
    if i % 2 == 0:
        continue
    print(i)

1
3
5
7
9

# 示例：使用 else 子句处理循环结束
for i in range(5):
    if i == 3:
        break
else:
    print("Loop completed normally")
print("After the loop")

0
1
2
After the loop

# 示例：使用列表推导式
squares = [x**2 for x in range(10)]
print(squares)

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# 示例：使用 while 循环
count = 0
while count < 5:
    print(count)
    count += 1

0
1
2
3
4

# 示例：使用 itertools.chain
import itertools

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined = itertools.chain(list1, list2)
for item in combined:
    print(item)

1
2
3
4
5
6

# 示例：使用 set 去重
numbers = [1, 2, 2, 3, 4, 4, 5]
unique_numbers = set(numbers)
print(unique_numbers)

{1, 2, 3, 4, 5}

# 示例：使用 dict.items 遍历键值对
person = {'name': 'Alice', 'age': 25, 'city': 'New York'}
for key, value in person.items():
    print(f"{key}: {value}")

name: Alice
age: 25
city: New York

# 示例：使用 try-except 处理异常
numbers = [1, 2, 3, 'four', 5]
for number in numbers:
    try:
        result = 10 / int(number)
        print(result)
    except ValueError:
        print(f"Invalid number: {number}")
    except ZeroDivisionError:
        print("Cannot divide by zero")

**10.**0
**5.**0
**3.**3333333333333335
Invalid number: four
**2.**0

# 示例：使用 sorted 排序
fruits = ['banana', 'apple', 'cherry']
sorted_fruits = sorted(fruits)
print(sorted_fruits)

['apple', 'banana', 'cherry']

# 示例：使用 reversed 反转
numbers = [1, 2, 3, 4, 5]
reversed_numbers = reversed(numbers)
for num in reversed_numbers:
    print(num)

5
4
3
2
1

# 示例：使用 filter 过滤
numbers = [1, 2, 3, 4, 5, 6]
even_numbers = filter(lambda x: x % 2 == 0, numbers)
print(list(even_numbers))

[2, 4, 6]

# 示例：使用 map 映射
numbers = [1, 2, 3, 4, 5]
squared_numbers = map(lambda x: x**2, numbers)
print(list(squared_numbers))

[1, 4, 9, 16, 25]

# 示例：使用 any 和 all 检查条件
numbers = [1, 2, 3, 4, 5]
contains_even = any(x % 2 == 0 for x in numbers)
all_positive = all(x > 0 for x in numbers)
print(f"Contains even: {contains_even}")
print(f"All positive: {all_positive}")

Contains even: True
All positive: True

# 示例：使用 reduce 进行累积操作
from functools import reduce
numbers = [1, 2, 3, 4, 5]
product = reduce(lambda x, y: x * y, numbers)
print(product)

120

# 示例：使用 asyncio 实现异步循环
import asyncio

async def print_numbers():
    for i in range(5):
        print(i)
        await asyncio.sleep(1)

asyncio.run(print_numbers())

0
1
2
3
4

import asyncio
import aiohttp
import os

async def download_image(session, url, filename):
    async with session.get(url) as response:
        if response.status == 200:
            with open(filename, 'wb') as f:
                f.write(await response.read())
            print(f"Downloaded {filename}")

async def main(urls, folder='images'):
    if not os.path.exists(folder):
        os.makedirs(folder)
    
    async with aiohttp.ClientSession() as session:
        tasks = []
        for i, url in enumerate(urls):
            filename = os.path.join(folder, f'image_{i}.jpg')
            task = asyncio.create_task(download_image(session, url, filename))
            tasks.append(task)
        
        await asyncio.gather(*tasks)

urls = [
    'https://example.com/image1.jpg',
    'https://example.com/image2.jpg',
    'https://example.com/image3.jpg'
]

asyncio.run(main(urls))