Symbols, Tickers & Lot Sizes

You'd think a stock would have one name. It doesn't. Reliance is RELIANCE to the NSE, RELIANCE.NS to Yahoo, RELIANCE.BO if you mean its BSE listing, and INE002A01018 to the settlement system. Apple is simply AAPL. Getting the symbol right is the difference between fetching real data and getting an empty result, so this short chapter makes symbols - and the F&O "lot" - second nature.

One company, many tickers

The same company carries different identifiers across systems, and you need to translate between them:

import yfinance as yf

# The same company wears different "names" on different systems.
def to_yahoo(symbol, exchange="NSE"):
    """Turn a plain NSE/BSE symbol into its Yahoo Finance ticker."""
    suffix = {"NSE": ".NS", "BSE": ".BO"}.get(exchange, "")
    return symbol + suffix

print("RELIANCE on NSE ->", to_yahoo("RELIANCE", "NSE"))   # RELIANCE.NS
print("RELIANCE on BSE ->", to_yahoo("RELIANCE", "BSE"))   # RELIANCE.BO
print("AAPL (US)       ->", to_yahoo("AAPL", "US"))        # AAPL (no suffix)
print()

# Fetch the latest close for each, proving the mapped symbols really work.
for label, ysym in [("RELIANCE (NSE)", "RELIANCE.NS"), ("Apple (US)", "AAPL")]:
    close = yf.Ticker(ysym).history(period="5d")["Close"].dropna()
    print(f"{label:16} last close: {round(float(close.iloc[-1]), 2)}")

RELIANCE on NSE -> RELIANCE.NS
RELIANCE on BSE -> RELIANCE.BO
AAPL (US)       -> AAPL

RELIANCE (NSE)   last close: 1313.6
Apple (US)       last close: 293.08

The rules are simple once you know them: Yahoo wants .NS for an NSE listing and .BO for a BSE one; US tickers (AAPL, MSFT) take no suffix; and an index starts with ^ (Chapter 33). A tiny mapping function like to_yahoo saves you from ever guessing - write it once, reuse it everywhere.

Lot sizes: trading in bundles

In the cash market you can buy a single share. But in futures and options, you trade fixed bundles called lots - you can't buy "one Nifty," only one lot of Nifty. The money at stake is the contract value: price times lot size:

# In F&O you trade fixed LOTS, not single shares. Contract value = price x lot size.
# (Lot sizes are illustrative - exchanges revise them periodically.)
lots = {"NIFTY": 75, "BANKNIFTY": 35, "RELIANCE": 500, "TCS": 175}
prices = {"NIFTY": 24021.65, "BANKNIFTY": 52000.00, "RELIANCE": 1313.60, "TCS": 2109.00}

print(f"{'Symbol':<12}{'Lot':>6}{'Price':>12}{'Contract value':>18}")
print("-" * 48)
for sym, lot in lots.items():
    value = lot * prices[sym]
    print(f"{sym:<12}{lot:>6}{prices[sym]:>12,.2f}{value:>18,.2f}")

Symbol         Lot       Price    Contract value
------------------------------------------------
NIFTY           75   24,021.65      1,801,623.75
BANKNIFTY       35   52,000.00      1,820,000.00
RELIANCE       500    1,313.60        656,800.00
TCS            175    2,109.00        369,075.00

A single Nifty lot controls over ₹18 lakh of index; a Reliance lot, around ₹6.5 lakh. That's no accident:

Mapping symbols in code

The practical takeaway is a habit: keep a small function (or dictionary) that converts between your symbol and whatever a data source expects. Your strategy code then speaks plain symbols - RELIANCE, AAPL - and the mapper handles the .NS, the .BO, the ^, or the format OpenAlgo wants. It's a five-line investment that pays off the moment you pull data from more than one place.

Try it yourself

• Extend to_yahoo to handle an index: if exchange == "INDEX", return the symbol unchanged (you'd pass ^NSEI directly).
• Use it to fetch TCS from the NSE (to_yahoo("TCS")) and confirm you get a real price back.
• In the lot-size table, add INFY with a lot of 400 at its current price, and read off its contract value.

Recap

• The same stock has different symbols per system; for Yahoo, .NS (NSE), .BO (BSE), no suffix (US), ^ (index).
• The ISIN is a single global identifier behind all the ticker variants.
• In F&O you trade lots; contract value = price x lot size, and lots are sized to a meaningful rupee value (and change over time).
• Keep a small mapping function so your code speaks plain symbols and adapts to any data source.

You can now name any instrument and find its data. Two more everyday practicalities separate a confident Indian-market coder from a confused one: the units (lakhs and crores, not millions) and the clock (9:15 IST, holidays and all). The next chapter handles money, timings and holidays.