如何修改嵌套For循环输出，匹配fill_values实现指定格式？

问题描述 #

我有一组用于填充缺失值的数据集：

In [1]: sex_class = ['female','male']
        pclass = [1,2,3]
        fill_values = [34,40,29,18,24,25]

In [2]: for i in pclass:
            for j in sex_class:
                print(i,j)
Out[2]: 1 female
        1 male
        2 female
        2 male
        3 female
        3 male

需要修改代码，让输出呈现为以下指定格式：

1 female 34
1 male   40
2 female 29
2 male   18
3 female 24
3 male   25

解决方案 #

方法1：使用索引计数器 #

引入一个索引变量，在每次循环中取出对应fill_values元素，同时用字符串格式化实现文本对齐：

sex_class = ['female','male']
pclass = [1,2,3]
fill_values = [34,40,29,18,24,25]

idx = 0
for i in pclass:
    for j in sex_class:
        # 左对齐第二列，固定宽度6个字符，保证male和female对齐
        print(f"{i} {j:<6} {fill_values[idx]}")
        idx += 1

方法2：先构建配对组合再遍历 #

先把pclass和sex_class的所有组合与fill_values配对，再循环输出，逻辑更直观：

sex_class = ['female','male']
pclass = [1,2,3]
fill_values = [34,40,29,18,24,25]

# 生成所有(pclass, sex)组合
combinations = []
for cls in pclass:
    for sex in sex_class:
        combinations.append((cls, sex))

# 组合对应的值并输出
for (cls, sex), val in zip(combinations, fill_values):
    print(f"{cls} {sex:<6} {val}")

方法3：用itertools.product简化组合生成 #

借助itertools.product可以快速生成pclass和sex_class的笛卡尔积，代码更简洁：

from itertools import product

sex_class = ['female','male']
pclass = [1,2,3]
fill_values = [34,40,29,18,24,25]

for (cls, sex), val in zip(product(pclass, sex_class), fill_values):
    print(f"{cls} {sex:<6} {val}")

内容的提问来源于stack exchange，提问作者Armando Bridena