for 循环

Python for Developers 入门

Jasmin Ludolf

Senior Data Science Content Developer

单个比较

# 配料数量
quantities = [500, 400, 15, 20, 30, 5]

# 验证数值
quantities[0] < 10

False

quantities[1] < 10

False

for 循环语法

for value in sequence:
    action

对 sequence 中的每个 value 执行 action
- 由于上一行的冒号，action 需缩进
sequence = 可迭代对象，如列表、字典等
value = 迭代变量，即索引
- 占位名（可任意命名），常用 i

打印单个值

# 配料列表
ingredients = ["pasta", "tomatoes", "garlic", "basil", "olive oil", "salt"]


# 遍历并打印每个配料
for ingredient in ingredients:

    print(ingredient)

pasta
tomatoes
garlic
basil
olive oil
salt

for 循环中的条件语句

quantities = [1000, 800, 40, 30, 30, 15]

for qty in quantities:

for 循环中的条件语句

quantities = [1000, 800, 40, 30, 30, 15]

for qty in quantities:

    # 检查数量是否大于 500
    if qty > 500:
      print("库存充足")
    elif qty >= 100:
        print("小份够用")
    else:
        print("快用完了！")

for 循环中的条件语句

库存充足
小份够用
快用完了！
快用完了！
快用完了！

遍历字符串

ingredient_name = "pasta"

# 遍历每个字符
for letter in ingredient_name:
    print(letter)

p
a
s
t
a

适用于验证文本、检查特殊字符

遍历字典

ingredients = {"pasta": 500, "tomatoes": 400, "garlic": 30}


# 同时遍历键和值
for item, qty in ingredients.items():
    print(item, ":", qty, "grams")

pasta : 500 grams
tomatoes : 400 grams
garlic : 30 grams

item = 键（配料名）
qty = 值（数量）

遍历字典

ingredients = {"pasta": 500, "tomatoes": 400, "garlic": 30}
factor = 2

# 计算缩放后的数量
for item, qty in ingredients.items():
    scaled_qty = qty * factor
    print(item, ":", scaled_qty, "grams")

pasta : 1000 grams
tomatoes : 800 grams
garlic : 60 grams

遍历字典

# 仅遍历键
for item in ingredients.keys():
    print(item)

pasta
tomatoes
garlic

# 仅遍历值
for qty in ingredients.values():
    print(qty, "grams")

500 grams
400 grams
30 grams

range

range(start, end + 1)

start = 起始数
end = 结束数
用于生成或修改数值

for i in range(1, 6):
    print(i)

让我们来练习！

Python for Developers 入门