如何创建含变量与注释的正则表达式？现有实现失效求助

Let's break down why your original regex wasn't working and fix it step by step.

Key Issues in Your Original Code #

1. Comments were swallowing your pattern: When you concatenated the strings without line breaks, the # study number comment continued through your doctype variable and into the next comment. In re.VERBOSE mode, anything after a # (not inside a character class) is treated as a comment until the end of the line—so your doctype and version sections were never actually part of the regex pattern!
2. Missing literal separators: VERBOSE mode ignores whitespace, so you need to explicitly include any required characters (like hyphens) between sections of your target string.
3. Unescaped variable risk: If your doctype contains regex special characters (e.g., ., *, +), it would break the regex unless escaped.

Corrected Code #

import re

# Example value for your doctype variable
doctype = "report"

# Properly structured regex with comments, variables, and VERBOSE mode
regex = re.compile(
    r'''
    ^(sm\d{5}-[a-z]+-\d{2})  # Capture the study number (format: smXXXXX-XXXX-XX)
    -                         # Hyphen separator between study number and doctype
    ''' + re.escape(doctype) + r'''  # Insert the document type variable (escaped for safety)
    -                         # Hyphen separator between doctype and version
    v(\d+)-(\d+)              # Capture major and minor version numbers (format: vXX-XX)
    \.pdf$                    # Match the literal .pdf file extension
    ''',
    re.VERBOSE
)

# Example usage
test_string = "sm12345-test-01-report-v01-02.pdf"
match = regex.match(test_string)

if match:
    print(f"Study Number: {match.group(1)}")
    print(f"Major Version: {match.group(2)}")
    print(f"Minor Version: {match.group(3)}")

What Changed? #

• Line breaks for comments: Each comment is now on its own line, so they don't interfere with the actual pattern parts.
• Explicit separators: Added - between sections (adjust this if your target string uses a different separator like _ or nothing).
• Escaped variable: Used re.escape(doctype) to ensure any special characters in your variable are treated as literal text, not regex operators.
• Cleaner structure: The regex is now easy to read and modify, thanks to VERBOSE mode and well-placed comments.

If your target string doesn't use hyphens between sections, just remove or replace the - characters in the pattern to match your actual format.

内容的提问来源于stack exchange，提问作者Manar