How to Build an AI Stock Picker in Python You Can Actually Audit

The model is the part everyone talks about. The data is the part that breaks.

Stock picking doesn't need more intelligence. It needs better inputs.

Best AI stock pickers vs building your own

Before writing code, it's worth being honest about the trade-off.

Best for: if you want a ready-made app, use one of the first three. If you want to know exactly why a stock ranks #1, and change it, build your own.

That's what we'll do now.

The data layer: EODHD APIs

I use EODHD APIs for this kind of project because one API key covers every input the AI stock picker needs:

• Stock Screener API to build the universe (filter by market cap, exchange, sector).
• Fundamentals API for ROE, revenue growth, margins and P/E.
• End-of-Day Historical Data API for adjusted prices, to calculate momentum.
• Financial News Sentiment API for a daily sentiment score per ticker.

Same JSON format, same authentication, same rate limits.

👉 You can get your EODHD API key here and follow along.

Build the AI stock picker in Python (step by step)

Install the dependencies:

pip install requests pandas python-dotenv openai

Create a .env file with your keys:

EODHD_API_KEY=your_eodhd_key
OPENAI_API_KEY=your_openai_key

And a small helper to call any EODHD endpoint:

import os, json
from datetime import date, timedelta

import requests
import pandas as pd
from dotenv import load_dotenv

load_dotenv(override=True)
EODHD_KEY = os.environ["EODHD_API_KEY"]
BASE = "https://eodhd.com/api"


def get(path, **params):
    params.update(api_token=EODHD_KEY, fmt="json")
    r = requests.get(f"{BASE}/{path}", params=params, timeout=30)
    r.raise_for_status()
    return r.json()

Step 1: Build the stock universe with the Screener API

We start with the 200 largest US stocks above $10B market cap. The Screener API returns up to 100 rows per call, so we paginate.

def build_universe(n=200):
    rows = []
    for offset in range(0, n, 100):
        rows += get(
            "screener",
            filters=json.dumps([
                ["market_capitalization", ">", 10_000_000_000],
                ["exchange", "=", "us"],
            ]),
            sort="market_capitalization.desc",
            limit=100,
            offset=offset,
        )["data"]
    df = pd.DataFrame(rows)[["code", "name", "sector", "market_capitalization", "adjusted_close"]]
    return df.drop_duplicates("code").reset_index(drop=True)

Step 2: Add fundamentals, momentum and news sentiment

Five features per stock. Each one maps to a classic factor:

def fundamentals(ticker):
    h = get(f"fundamentals/{ticker}.US", filter="Highlights")
    return {
        "roe": h.get("ReturnOnEquityTTM"),
        "rev_growth": h.get("QuarterlyRevenueGrowthYOY"),
        "margin": h.get("ProfitMargin"),
        "pe": h.get("PERatio"),
    }


def momentum(ticker):
    """6-month return, skipping the most recent month (classic 6-1 momentum)."""
    start = (date.today() - timedelta(days=200)).isoformat()
    px = pd.DataFrame(get(f"eod/{ticker}.US", **{"from": start}))["adjusted_close"]
    if len(px) < 130:
        return None
    return px.iloc[-22] / px.iloc[-130] - 1


def sentiment(tickers):
    """Average news sentiment over the last 30 days."""
    start = (date.today() - timedelta(days=30)).isoformat()
    out = {}
    for i in range(0, len(tickers), 20):
        batch = [f"{t}.US" for t in tickers[i:i + 20]]
        data = get("sentiments", s=",".join(batch), **{"from": start})
        for sym, days in data.items():
            if days:
                out[sym.split(".")[0]] = sum(d["normalized"] for d in days) / len(days)
    return out

Why skip the last month in momentum? Short-term returns tend to mean-revert. The 6-1 window is the standard way to capture trend without that noise.

Here's the real output of steps 1 and 2:

One ticker failed: VTI. It's an ETF, so it has no company fundamentals. The try/except skipped it and the run continued with 199 stocks.

Step 3: Score every stock

No neural network here. Each feature becomes a percentile rank (0 to 1), multiplied by a weight. The sum is a score from 0 to 100.

WEIGHTS = {"momentum": 0.25, "quality": 0.25, "growth": 0.20, "value": 0.15, "sentiment": 0.15}


def score(df):
    df = df[df["pe"].fillna(0) > 0].copy()  # drop loss-makers and missing P/E
    df["rel_pe"] = df["pe"] / df.groupby("sector")["pe"].transform("median")

    ranks = pd.DataFrame({
        "momentum": df["momentum"].rank(pct=True),
        "quality": df["roe"].rank(pct=True),
        "growth": df["rev_growth"].rank(pct=True),
        "value": (-df["rel_pe"]).rank(pct=True),
        "sentiment": df["sentiment"].rank(pct=True),
    }).fillna(0.5)

    for f, w in WEIGHTS.items():
        df[f"s_{f}"] = ranks[f] * w * 100
    df["score"] = df[[f"s_{f}" for f in WEIGHTS]].sum(axis=1).round(1)
    return df.sort_values("score", ascending=False).reset_index(drop=True)

Two design choices matter here:

• Value is relative to the sector. A P/E of 25 is cheap for a chip designer and expensive for a bank.
• Missing data gets a neutral 0.5. A stock isn't punished or rewarded for a gap in coverage.

This is the result. 194 stocks survived the P/E filter:

And the same ranking as a chart, so you can see which factor drives each score:

SanDisk and Micron get there with strength on every factor. Recruit Holdings (RCRUY) is the opposite case: top-tier momentum and sentiment, but almost nothing from value. Its P/E is 3.16x its sector median.

That's the kind of insight you never get from a single score.

Step 4: Let the LLM explain, not pick

This is where most "AI stock picker" tutorials go wrong. They ask the LLM to choose stocks.

We do the opposite. The model has already picked. ChatGPT only gets the numbers for one stock and writes the thesis.

from openai import OpenAI


def explain(row):
    facts = {
        "ticker": row["code"], "name": row["name"], "sector": row["sector"],
        "score": row["score"],
        "momentum_6_1": round(row["momentum"], 3),
        "roe_ttm": row["roe"], "revenue_growth_yoy": row["rev_growth"],
        "profit_margin": row["margin"], "pe": row["pe"],
        "pe_vs_sector_median": round(row["rel_pe"], 2),
        "news_sentiment_30d": round(row["sentiment"], 3) if pd.notna(row["sentiment"]) else None,
    }
    prompt = (
        "You are an equity analyst. Using ONLY the data below, write a 4-sentence "
        "investment thesis: why the model ranks this stock highly, and the main risk. "
        "Do not use any number that is not in the data. Ratios are decimals "
        "(0.25 = 25%): write them as percentages.\n\n" + json.dumps(facts, indent=2)
    )
    resp = OpenAI().responses.create(model="gpt-5.4-mini", input=prompt)
    return resp.output_text

The real output for the top 3:

Read it carefully, because there's a lesson in it.

The theses are grounded. Every number comes from our data. But the LLM still made two small mistakes:

• It wrote SanDisk's sentiment score (0.735) as "73.5%". Sentiment isn't a ratio.
• It left Dell's momentum as "a 1.635 gain" instead of 163.5%.

No invented P/E ratios. No hallucinated earnings. Just formatting slips that a reviewer catches in seconds.

Constrain the LLM to your data and its errors become cosmetic instead of dangerous.

What the AI stock picker taught me

The most useful output wasn't the #1 pick. It was this chart:

Technology is 20.6% of the universe. It's 85% of the top 20 picks (17 out of 20).

The model isn't broken. Memory, storage and semiconductor equipment stocks lead on momentum, growth and sentiment at the same time right now. A factor model rewards exactly that.

But if you bought the top 20 blindly, you wouldn't own a diversified portfolio. You'd own one big bet on the AI hardware cycle.

There's a second, smaller catch. ASML appears twice in the top 20: ASML (the US listing) and ASMLF (the OTC line). Same company, two tickers. Deduplicating by company is a one-line fix once you see it.

A black-box AI stock picker would have shown you neither problem.

From here you can build:

• Sector-neutral ranking: score stocks within each sector, then take the top 2 per sector.
• Different universes: swap the Screener filter for European stocks, dividend payers or small caps.
• A weekly alert: run the script on a schedule and email the top 10.

Limitations to be honest about

• This is not a backtest. The scores use today's fundamentals. Testing them on past prices would leak future information. A real backtest needs point-in-time fundamentals and delisted stocks to avoid survivorship bias.
• API usage adds up. A full run of 200 stocks costs roughly 2,000+ EODHD API calls, because each fundamentals request counts as 10 calls. The free plan is for testing, not for this.
• Weights are a choice, not a truth. 25/25/20/15/15 is a sensible default. Change them and the ranking changes.

Key takeaways

• An AI stock picker is data + scoring + explanation. The edge comes from the data, not from the model.
• Use the LLM to explain picks from real numbers, never to choose them.
• Transparency lets you spot problems, like 85% sector concentration, before they cost you money.

FAQs

❓ Is there a free AI stock picker? ✅ Yes. Prospero.ai offers a free app, and Danelfin and Kavout have free tiers with limited rankings. If you want full control, the Python script in this article is free to run. You only pay for the data API and a few cents of LLM usage.

❓ Can ChatGPT pick stocks? ✅ Not reliably on its own. Without live data, ChatGPT can quote outdated or invented numbers. It works well as an explanation layer when you give it real, current data from an API, like we did in Step 4.

❓ Are AI stock pickers accurate? ✅ No AI stock picker can guarantee returns. Factor models like this one rank stocks on characteristics that have historically mattered (momentum, quality, value), but the only way to judge accuracy is a proper backtest with point-in-time data.

❓ What data does an AI stock picker need? ✅ At minimum: price history for momentum, fundamentals (ROE, growth, valuation) and ideally news sentiment. EODHD covers all of them through one API key.

Final thoughts

Most investors don't need a smarter AI stock picker.

They need one they can see inside.

In the next article of this series, we go from ranking hundreds of stocks to analyzing one in depth: AI stock analysis with an LLM and real financial statements.

👉 Start building with EODHD APIs: Screener, Fundamentals, EOD prices and News Sentiment with one key. Use the code KEVIN10 at checkout for 10% off.

Disclaimer: This article is for educational purposes only and is not investment advice. The rankings shown are the output of an example model on November 1, 2026.

Looking for technical content for your company? I can help — LinkedIn · kevinmenesesgonzalez@gmail.com