FIX Protocol Tag=Value Pair Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching fix protocol tag=value pair, ported and verified for Python. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# FIX Protocol Tag=Value Pair
# ReDoS-safe | RegexVault — Finance > Securities & Trading

import re

fix_protocol_tagvalue_pair_pattern = re.compile(r'^[0-9]+=[^\x01\s]+$')

def validate_fix_protocol_tagvalue_pair(value: str) -> bool:
    return bool(fix_protocol_tagvalue_pair_pattern.fullmatch(value))

# Example
print(validate_fix_protocol_tagvalue_pair("35=D"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Securities & Trading category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

FIX protocol separates fields with SOH (\x01, ASCII 001). This pattern matches a single field — strip the SOH delimiter before matching individual pairs. Capture group 1: tag number, group 2: value. Tag 35 is MsgType.