Python迭代N嵌套循环？

Question

我有一个具有N个键列的CSV文件，并且该列的表达式包含对键列的1到N的引用，我希望将其替换为该行的每个键列中的值。希望下面的示例阐明我的意思。

下面的关键列是A，B，C

所需的输出：

20_A
20_B
30_A
30_B
40_C_4
40_C_5

我的解决方案：

keys = ['Age','Type','Delay']
df = pd.read_csv(csv_path)
for index, row in df.iterrows():

    key1_list = row[keys[0]].split(",")
    key2_list = row[keys[1]].split(",")
    key3_list = row[keys[2]].split(",")

    expression = row['Expression']

    # Iterate over all combinations of key column values and export a chart for each one
    for KEY1 in key1_list:
        for KEY2 in key2_list:
            for KEY3 in key3_list:
                string = expression
                string = string.replace("<" + keys[0] + ">", KEY1)
                string = string.replace("<" + keys[1] + ">", KEY2)
                string = string.replace("<" + keys[2] + ">", KEY3)
                print(string)

但是，我想概括一下我的代码以适用于任意数量的键列，并且只需要在开始时更新键列表。这将需要循环到深度len（keys）。但是我无法弄清楚如何使用平面代码将循环概括到任何深度，我看着itertools，但是找不到我需要的东西。我认为递归可能有效，但我更希望避免这种情况。

Answer 1

递归当然可以为您解决问题，但是在走那条路之前，您应该在itertools中进行另一番研究。您想要的是密钥的乘积，以生成所有可能的密钥组合。

一种实现方法如下：

import pandas as pd
import itertools

csv_path = "path/to/file"
df = pd.read_csv(csv_path)

# Find available keys from data frame instead of manually input it:
keys = list(df.keys()[:-1]) # Do not include "Expression" as it is not a key.
for index, row in df.iterrows():

    # Add list of keys to a list of lists
    # (The order needs to be preserved, therefore avoiding dict)
    key_list = []
    for key in keys:
        # The code uses ',' as value separator in each cell.
        # Does this work in a csv file?
        key_list.append(list(row[key].split(',')))

    expression = row['Expression']

    # All key combinations are then generated with 'itertools.product'
    combos = itertools.product(*key_list)

    # Each combo is then handled separately
    for combo in combos:
        string = expression
        # Replace each key in order
        # Must be done sequentially since depth is not known/variable
        for key, value in zip(keys, combo):
            string = string.replace('<' + key + '>', value)
        print(string)

希望这段代码是可以理解的，并且可以实现您想要的功能。否则，请告知我，我将尝试进一步澄清。