4. Professional data providers: beyond Yahoo Finance

Level 3: Market Data and APIs

yfinance is free and good enough for learning and for personal backtests, but it has limits: the data may arrive delayed, availability is not contractually guaranteed, and coverage of fundamental or alternative data is limited. When a project goes from being a personal experiment to something professional, paid providers come into play.

Intrinio offers real-time and historical quotes, company fundamentals and more than 200 different financial data sources, accessible both through bulk CSV download and through an API — the same data exchange mechanism you already use with yfinance, only paid for and with service guarantees.

Quandl (now part of Nasdaq Data Link) is one of the reference platforms for financial, economic and alternative data, used by analysts at investment funds, asset managers and investment banks. It is accessed just like any other Python library, with an API key:

import quandl

msft_data = quandl.get("WIKI/MSFT", start_date="2014-01-01", end_date="2016-01-01")

Choosing between a free provider such as yfinance and a paid one such as Intrinio or Quandl is not a question of which is 'better' in the abstract, it is a question of what you need it for: for learning and testing ideas, yfinance is more than enough; for trading real money seriously, the reliability and support of a paid provider usually justify the cost.