代码示例1：

import pandas as pd

# 读入两个文件
df1 = pd.read_csv('file1.csv')
df2 = pd.read_csv('file2.csv')

# 比较两个文件的列，并更改第二个文件匹配行的第二列字符串
for index, row1 in df1.iterrows():
    for index2, row2 in df2.iterrows():
        if row1['column1'] == row2['column1']:
            df2.at[index2, 'column2'] = 'new string'

# 将更改后的 df2 输出为新文件
df2.to_csv('file3.csv', index=False)

代码示例2：

with open('file1.csv', 'r') as f1:
    f1_lines = f1.readlines()

with open('file2.csv', 'r') as f2:
    f2_lines = f2.readlines()

# 比较两个文件的列，并更改第二个文件匹配行的第二列字符串
for i, line1 in enumerate(f1_lines):
    for j, line2 in enumerate(f2_lines):
        if line1.split(',')[0] == line2.split(',')[0]:
            f2_lines[j] = line2.replace(line2.split(',')[1], 'new string')

# 将更改后的 f2_lines 输出为新文件
with open('file3.csv', 'w') as f3:
    f3.writelines(f2_lines)