annotated_types.py

from typing import Annotated
from pydantic import Field

from pydantic_ai import Agent

# the Field description is respected by the LLM as it produces a list[HistoricEvent]
HistoricEvent = Annotated[str, Field(description="what, where, when, how, why - very concise")]

historic_event_brainstormer = Agent[None, list[HistoricEvent]](
    "openai:gpt-4o",
    system_prompt="think of events from the last 300 years",
    result_type=list[HistoricEvent]
)

result = historic_event_brainstormer.run_sync("wars between the US and Europe")
print(result.data)
"""
['1775-1783: American Revolutionary War: The thirteen American colonies fought against British rule to gain independence.', '1812-1815: War of 1812: The United States declared war on the United Kingdom over maritime rights and territorial expansion.', '1917-1918: World War I: The US joined the Allied Powers to fight against the Central Powers, including Germany, primarily in Europe.', '1941-1945: World War II: The US fought as part of the Allied Powers against the Axis Powers, including Nazi Germany, primarily in Europe.', '1999: Kosovo War: The US, within NATO, conducted a bombing campaign against Yugoslavia to halt human rights abuses in Kosovo.']
"""