SEDOL Validation in Python

1. What is a SEDOL?

A SEDOL (Stock Exchange Daily Official List) is a 7-character alphanumeric identifier assigned by the London Stock Exchange Group (LSEG) to securities. Introduced in 1979, SEDOLs are the primary identifier in the UK financial infrastructure — used by settlement systems, regulatory filings, and data vendors alike.

CREST (the UK and Irish central securities depository, operated by Euroclear) references SEDOLs in settlement instructions. The FCA requires SEDOLs in MiFIR transaction reports alongside ISINs. The SEDOL Masterfile — the authoritative source maintained by LSEG — contains over 100 million securities from exchanges worldwide.

Despite its UK origins, SEDOL is widely used in global financial data pipelines, particularly for European and international equities processed through UK-based custodians and prime brokers.

2. SEDOL anatomy

Every SEDOL is exactly 7 characters: 6 alphanumeric base characters followed by a 1-digit check digit.

Some well-known examples:

3. The check digit algorithm

The SEDOL check digit uses a weighted modulo-10 algorithm with fixed position weights [1, 3, 1, 7, 3, 9]. Character values: digits 0–9 map to 0–9, letters A–Z map to 10–35 (A=10, B=11, … Z=35).

Steps:

1. Convert each of the first 6 characters to its numeric value.
2. Multiply each value by the corresponding weight from [1, 3, 1, 7, 3, 9].
3. Sum all 6 products to get S.
4. Check digit = (10 - S % 10) % 10.

Here is what a naive Python implementation looks like:

# sedol_check.py — naive implementation (format + check digit only)
import re

WEIGHTS = [1, 3, 1, 7, 3, 9]
SEDOL_RE = re.compile(r'^[A-Z0-9]{6}[0-9]$')


def char_value(ch: str) -> int:
    """Return numeric value of a SEDOL character.
    Digits 0-9 → 0-9, letters A-Z → 10-35.
    """
    if ch.isdigit():
        return int(ch)
    if ch.isalpha():
        return ord(ch) - ord('A') + 10
    raise ValueError(f"Invalid SEDOL character: {ch!r}")


def compute_check_digit(base6: str) -> int:
    """Compute the SEDOL check digit for the first 6 characters."""
    total = sum(char_value(base6[i]) * WEIGHTS[i] for i in range(6))
    return (10 - total % 10) % 10


def validate_sedol(sedol: str) -> dict:
    sedol = sedol.replace(' ', '').upper()

    if len(sedol) != 7 or not SEDOL_RE.match(sedol):
        return {'valid': False, 'reason': 'format'}

    expected = compute_check_digit(sedol[:6])
    actual = int(sedol[6])

    if expected != actual:
        return {'valid': False, 'reason': 'check_digit'}

    return {
        'valid': True,
        'sedol': sedol,
        'check_digit': sedol[6],
    }


# ── Examples ──────────────────────────────────────────────────────────────────
print(validate_sedol('0798059'))   # valid — BP PLC
print(validate_sedol('0540528'))   # valid — HSBC Holdings
print(validate_sedol('0798051'))   # invalid check digit
print(validate_sedol('07980'))     # invalid format

4. Why manual validation is not enough

5. The right solution: one API call

The IsValid SEDOL API combines format validation, check digit verification, and live OpenFIGI enrichment in a single GET /v0/sedol request.

Get your free API key at isvalid.dev.

Full parameter reference and response schema: SEDOL Validation API docs →

6. Python code example

Using the isvalid-sdk package or the requests library directly.

# sedol_validator.py
import os
from isvalid_sdk import IsValid

iv = IsValid(api_key=os.environ["ISVALID_API_KEY"])

# ── Example usage ─────────────────────────────────────────────────────────────

result = iv.sedol("0798059")  # BP PLC

if not result["valid"]:
    print("Invalid SEDOL: failed format or check digit")
else:
    print(f"SEDOL       : {result['sedol']}")
    print(f"Check digit : {result['checkDigit']}")
    if result.get("found"):
        print(f"Name        : {result.get('name')}")
        print(f"Ticker      : {result.get('ticker')}")
        print(f"Exchange    : {result.get('exchCode')}")
        print(f"FIGI        : {result.get('figi')}")
        print(f"Sector      : {result.get('marketSector')}")

Expected output for 0798059:

SEDOL       : 0798059
Check digit : 9
Name        : BP PLC
Ticker      : BP/
Exchange    : LN
FIGI        : BBG000BT4FC2
Sector      : Equity

# views.py (Django) / router.py (FastAPI)
from fastapi import APIRouter, HTTPException
import requests, os

router = APIRouter()
API_KEY = os.environ["ISVALID_API_KEY"]


@router.get("/securities/validate-sedol")
def validate_sedol_endpoint(sedol: str):
    if not sedol:
        raise HTTPException(status_code=400, detail="Missing sedol parameter")

    try:
        resp = requests.get(
            "https://api.isvalid.dev/v0/sedol",
            params={"value": sedol},
            headers={"Authorization": f"Bearer {API_KEY}"},
            timeout=10,
        )
        resp.raise_for_status()
        result = resp.json()
    except requests.RequestException:
        raise HTTPException(status_code=502, detail="SEDOL validation service unavailable")

    if not result["valid"]:
        raise HTTPException(status_code=400, detail=f"Invalid SEDOL: {sedol}")

    return {
        "sedol": result["sedol"],
        "checkDigit": result["checkDigit"],
        "found": result.get("found"),
        "name": result.get("name"),
        "ticker": result.get("ticker"),
        "exchCode": result.get("exchCode"),
        "figi": result.get("figi"),
    }

7. cURL example

Validate a SEDOL from the command line:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/sedol?value=0798059"

HSBC Holdings:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/sedol?value=0540528"

Invalid check digit:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/sedol?value=0798051"

8. Understanding the response

Response for a valid SEDOL found in OpenFIGI:

{
  "valid": true,
  "sedol": "0798059",
  "checkDigit": "9",
  "found": true,
  "dataSource": "openfigi",
  "name": "BP PLC",
  "ticker": "BP/",
  "exchCode": "LN",
  "securityType": "Common Stock",
  "marketSector": "Equity",
  "figi": "BBG000BT4FC2",
  "compositeFIGI": "BBG000BT4FC2"
}

Response for an invalid SEDOL:

{
  "valid": false
}

9. Edge cases to handle

10. Summary

• ISIN validation — ISINs embed SEDOLs for GB-prefixed codes
• CUSIP validation — the North American equivalent
• SEDOL Validation in Node.js