Pulling the first period where index constituents are available

Amor

I have this working code to identify when is the first period that the constituent lists has data. It correctly states that the oldest constituent list avaialble for S&P 500 (list code LS&PCOMP+MMYY) is 0989 or September 1989. How do I apply this code to multiple constituent codes for around 90 indices?

from datetime import datetime
from dateutil.relativedelta import relativedelta
import pandas as pd

def find_earliest_constituent_date(index_prefix, start_mmyy):
current_date = datetime.strptime(start_mmyy, "%m%y")
last_valid_date = None

while True:

    mmyy = current_date.strftime("%m%y")

    ticker = f"{index_prefix}{mmyy}|L"

    print(f"Checking: {ticker}")


    try:

        result = ds.get_data(tickers=ticker, fields=["MNEM"], kind=0)


        # Check if Value column contains any actual data (not NA or empty)

        if isinstance(result, pd.DataFrame) and "Value" in result.columns:

            values = result["Value"].dropna().astype(str).str.strip()

            if not values.eq("NA").all() and not values.eq("").all():

                last_valid_date = current_date

                current_date -= relativedelta(months=1)

                continue


        # All values are NA or empty — stop and return last valid

        if last_valid_date:

            earliest_mmyy = last_valid_date.strftime("%m%y")

            print(f"\n✅ Earliest available constituent list: {index_prefix}{earliest_mmyy}|L")

            return earliest_mmyy

        else:

            print("⚠️ No valid data found at all.")

            return None


    except Exception as e:

        print(f"Error querying {ticker}: {e}")

        return None

Example usage

find_earliest_constituent_date("LS&PCOMP", "0191") # Start from Jan 1991