Bitcoin Address (Legacy P2PKH — starts with 1) Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching bitcoin address (legacy p2pkh — starts with 1), 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

# Bitcoin Address (Legacy P2PKH — starts with 1)
# ReDoS-safe | RegexVault — Finance > Crypto

import re

bitcoin_address_legacy_p2pkh_starts_with_1_pattern = re.compile(r'^1[a-km-zA-NP-Z1-9]{25,34}$')

def validate_bitcoin_address_legacy_p2pkh_starts_with_1(value: str) -> bool:
    return bool(bitcoin_address_legacy_p2pkh_starts_with_1_pattern.fullmatch(value))

# Example
print(validate_bitcoin_address_legacy_p2pkh_starts_with_1("1A1zP1eP5QGefi2DMPTfTL5SLmv7Divf"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Crypto 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

P2PKH addresses start with 1. Base58Check encoding (excludes 0, O, I, l to avoid confusion). Length is 25-34 chars. The address encodes a hash of the public key — validate the checksum with actual Base58Check decoding.