python学习之for i in...

前言：以python经常就见见for i in range()和字符串之类的，但是最近有遇到了许多列表，所以打算记录整理一下

在 Python 中，for 循环可以用来遍历任何可迭代的对象。除了 range() 之外，还有很多其他的数据类型和结构可以用于 for 循环。

1.遍历字符串

text = "hello world"

for char in text:

print(char, end=' ')

# 输出: h e l l o w o r l d

2. 遍历列表

numbers = [1, 2, 3, 4, 5]

for num in numbers:

print(num, end=' ')

# 输出: 1 2 3 4 5

3.遍历元组

tup = (10, 20, 30, 40, 50)

for item in tup:

print(item, end=' ')

# 输出: 10 20 30 40 50

4.遍历字典

字典可以通过 keys(), values(), 或 items() 方法来遍历：

dict_data = {'a': 1, 'b': 2, 'c': 3}
for key in dict_data.keys():print(key, end=' ')# 输出: a b cfor value in dict_data.values():print(value, end=' ')# 输出: 1 2 3for key, value in dict_data.items():print(f"{key}: {value}", end=' ')# 输出: a: 1 b: 2 c: 3

5.遍历集合

set_data = {1, 2, 3, 4, 5}

for element in set_data:

print(element, end=' ')

# 输出: 1 2 3 4 5 （顺序不定）

6.遍历文件

with open('example.txt', 'r') as file:

for line in file:

print(line, end='')

# 输出: 文件中的每一行内容

7.遍历自定义可迭代对象

class MyIterable:def __init__(self, data):self.data = datadef __iter__(self):return iter(self.data)my_iterable = MyIterable([1, 2, 3, 4, 5])
for item in my_iterable:print(item, end=' ')
# 输出: 1 2 3 4 5

8.使用 `enumerate` 遍历序列并获取索引

words = ["apple", "banana", "cherry"]
for index, word in enumerate(words):print(f"Index {index}: {word}")
# 输出:
# Index 0: apple
# Index 1: banana
# Index 2: cherry

9.使用zip同时遍历多个序列

names = ["Alice", "Bob", "Charlie"]
ages = [25, 30, 35]
for name, age in zip(names, ages):print(f"{name} is {age} years old.")
# 输出:
# Alice is 25 years old.
# Bob is 30 years old.
# Charlie is 35 years old.

10.使用 `filter` 和 `map` 遍历序列并处理数据

numbers = [1, 2, 3, 4, 5]
even_numbers = filter(lambda x: x % 2 == 0, numbers)
for num in even_numbers:print(num, end=' ')
# 输出: 2 4squared_numbers = map(lambda x: x ** 2, numbers)
for num in squared_numbers:print(num, end=' ')
# 输出: 1 4 9 16 25