How to Fix Pandas Prefix Matching to Retrieve Specific Columns in Excel Data

1. Preface

Hello, I am a Python intermediate user. Recently I asked a question in a Python automation group about why a pandas prefix‑matching operation did not return the expected column values.

The problem description was:

"Why does this matching not work? Matching from the start of the string should return the specified column value, but it fails." Here is the original code:

import pandas as pd
file = r"C:\Users\admin\Desktop\2024-11-29漏洞规整.xlsx"

df1 = pd.read_excel(file, sheet_name="表1")
df2 = pd.read_excel(file, sheet_name="表2")

def find_matching_b(value, df2):
    matched = df2[df2['版本'].str.startswith(value)]
    if not matched.empty:
        return matched['漏洞名称'].iloc[0]  # return first match's B column value
    return None

df1['漏洞版本规整'] = df1['参考验证信息'].apply(lambda x: find_matching_b(x, df2))

2. Implementation Process

A fellow group member pointed out that the matching condition was reversed. After correcting the logic, the code works as intended and the issue is resolved.

3. Summary

The article demonstrates a typical pandas string‑matching problem in Excel data processing, provides the faulty code, explains the logical error, and presents the corrected implementation. It also offers practical tips for asking technical questions: anonymize large data, provide minimal reproducible examples, include error screenshots, and share code directly when it is short.