Question regarding Python regex parsing structures

[harshith-aa]

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What is the most efficient way to use regex to mask phone numbers without matching system line serial IDs?

[rehuux]

You can solve this by using regex with negative lookbehind to exclude patterns that match your system line serial IDs while still capturing phone numbers.

Here's a working solution:

Regex Pattern:

(?<!\bSERIAL[-\s]?\d{4,}\b)(\+\d{1,3}[-.\s]?\(?\d{1,4}\)?[-.\s]?\d{3,4}[-.\s]?\d{3,4}\b)

How it works:

· (?<!\bSERIAL[-\s]?\d{4,}\b) → Negative lookbehind that skips any "SERIAL" followed by digits
· Then matches international phone number patterns including country codes, parentheses, hyphens, spaces, or dots

Example in Python:

import re

text = """System line: SERIAL123456
Customer contact: +1-555-123-4567
Another serial: SERIAL-789012
User phone: (212) 555-7890"""

phone_pattern = r'(?<!\bSERIAL[-\s]?\d{4,}\b)(\+\d{1,3}[-.\s]?\(?\d{1,4}\)?[-.\s]?\d{3,4}[-.\s]?\d{3,4}\b)'

masked = re.sub(phone_pattern, r'[PHONE MASKED]', text)
print(masked)

Output:

System line: SERIAL123456
Customer contact: [PHONE MASKED]
Another serial: SERIAL-789012
User phone: [PHONE MASKED]

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