SemVer Pre-Release Identifier Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching semver pre-release identifier, ported and verified for Python. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. 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

# SemVer Pre-Release Identifier
# ReDoS-safe | RegexVault — Dev & Systems > SemVer

import re

semver_prerelease_identifier_pattern = re.compile(r'^(?:0|[1-9][0-9]*|[0-9]*[a-zA-Z][a-zA-Z0-9\-]*)(?:\.(?:0|[1-9][0-9]*|[0-9]*[a-zA-Z][a-zA-Z0-9\-]*))*$')

def validate_semver_prerelease_identifier(value: str) -> bool:
    return bool(semver_prerelease_identifier_pattern.fullmatch(value))

# Example
print(validate_semver_prerelease_identifier("alpha"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > SemVer 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

Numeric identifiers must not have leading zeros (01 is invalid). Alphanumeric identifiers have lower precedence than numeric ones in version comparison.