09Build Your First Agent

ollama pull qwen3:8b
mkdir invoice-agent && cd invoice-agent
python -m venv .venv
source .venv/bin/activate        # Windows: .venv\Scripts\activate
pip install ollama

id,client,email,amount_php,due_date,status
1041,Kapé Iloilo,[email protected],12500,2026-08-30,paid
1042,Maria Santos,[email protected],18500,2026-09-10,unpaid
1043,Island Supply Co.,[email protected],7200,2026-09-18,unpaid
1044,Dr. Reyes Dental,[email protected],25000,2026-10-15,unpaid

import csv, datetime, json
import ollama

MODEL = "qwen3:8b"
TODAY = datetime.date(2026, 9, 27)   # fixed for the demo; use date.today() in real life

# ---------------- TOOLS: plain Python functions -----------------
# The docstring and type hints become the tool description the model reads.

def list_invoices(status: str = "unpaid") -> str:
    """List invoices filtered by status ('paid', 'unpaid' or 'all').
    Returns id, client, email, amount in PHP, due date and days overdue."""
    rows = []
    with open("invoices.csv", newline="") as f:
        for r in csv.DictReader(f):
            if status != "all" and r["status"] != status:
                continue
            due = datetime.date.fromisoformat(r["due_date"])
            r["days_overdue"] = max(0, (TODAY - due).days)
            rows.append(r)
    return json.dumps(rows)

def draft_email(to: str, subject: str, body: str) -> str:
    """Save a draft email for the owner to review. Use for every reminder.
    Does NOT send anything."""
    DRAFTS.append({"to": to, "subject": subject, "body": body})
    return f"Draft #{len(DRAFTS)} saved for {to}."

def send_email(draft_number: int) -> str:
    """Send a previously saved draft by its number. Requires human approval."""
    d = DRAFTS[draft_number - 1]
    print("\n" + "=" * 60)
    print(f"TO: {d['to']}\nSUBJECT: {d['subject']}\n\n{d['body']}")
    print("=" * 60)
    if input("Approve sending this email? [y/N] ").strip().lower() != "y":
        return "Owner declined. Do not send; ask what to change."
    with open("outbox.log", "a") as log:            # stand-in for a real email API
        log.write(json.dumps(d) + "\n")
    return f"Draft #{draft_number} sent to {d['to']}."

TOOLS = {f.__name__: f for f in [list_invoices, draft_email, send_email]}
DRAFTS = []

SYSTEM = f"""You are the back-office assistant for a freelance web designer.
Today is {TODAY.isoformat()}.
- Always use tools to get facts. Never invent amounts, dates or emails.
- For overdue invoices, draft a short, friendly, professional reminder
  (under 120 words) that states the invoice number, amount and due date.
- Only call send_email after drafting. If the owner declines, stop and ask.
- When finished, give a one-paragraph summary of what you did."""

# ---------------- THE AGENT LOOP -----------------
def run(goal: str, max_steps: int = 15):
    messages = [{"role": "system", "content": SYSTEM},
                {"role": "user", "content": goal}]
    for step in range(1, max_steps + 1):
        response = ollama.chat(model=MODEL, messages=messages,
                               tools=list(TOOLS.values()))
        msg = response.message
        messages.append(msg)

        if not msg.tool_calls:                      # no tool requested → final answer
            print("\n🤖", msg.content)
            return

        for call in msg.tool_calls:
            name, args = call.function.name, call.function.arguments
            print(f"🔧 step {step}: {name}({args})")
            try:
                result = TOOLS[name](**args)
            except Exception as e:                   # helpful errors let it recover
                result = f"error: {e}"
            messages.append({"role": "tool", "content": str(result), "tool_name": name})

    print("⚠️ Stopped: step limit reached.")        # guardrail

if __name__ == "__main__":
    run(input("What should I do? "))

python agent.py
What should I do? Find overdue invoices and chase them politely.