By using the Literal type from the Python typing library, you can define a valid list of values that get rendered as a drop-down list in the prefect UI.
Example:
from prefect import flow
from typing import Literal
DropDownChoices = Literal["Prefect", "Python", "Pizza"]
@flow(name="Print-Drop-Down-Flow", log_prints=True)
def print_drop_down_flow(drop_down_choice: DropDownChoices = "Prefect"):
print(f"The drop down choice was: {drop_down_choice}")
if __name__ == "__main__":
# create your first deployment
print_drop_down_flow.serve(name="Print-Drop-Down-Deployment")
