How to run python scripts with default arguments in FastAPI?

Question

I am new to FastAPI and I would like to ask for some explanation.

My code:

app_code.py:

import json
import argparse


def args():
    parser = argparse.ArgumentParser("Some argumets")
    parser.add_argument("--name", type=str)
    parser.add_argument("--surname", type=str, nargs='?', default="Smith")
    parser.add_argument("--birthday", type=str, nargs='?', default="2001")

    args = parser.parse_args()
    return args


def create_df(name):
    ar = args()
    print(ar)
    x = {"name": name, "surname": ar.surname, "bd": ar.birthday}

    x = json.dumps(x)

    return x


if __name__ == "__main__":
    args_all = args()

    print(f"name: {args_all.name}, surname: {args_all.surname}, birthday:{args_all.birthday}")
    print(create_df(args_all.name))

main_api.py

from fastapi import FastAPI
from app_code import *

app = FastAPI()


@app.get("/names")
async def root(name: str = 'none'):
    print("In progress...")
    result = create_df(name)
    return result

When I run it normally, I mean run just script app by:

python app_code.py --name=James

I got proper result:

{name:James, surname:Smith, bd:2001}

But I have problems with arguments when I use it as a FastAPI web application. i.e., when I go to the browser and access:

api.addres.url/port/name?James

I got that error:

 File "P:\pythonProject3\api\.\app_code.py", line 16, in create_df
    ar = args()
  File "P:\pythonProject3\api\.\app_code.py", line 11, in args
    args = parser.parse_args()
  File "C:\Users\ubunt\AppData\Local\Programs\Python\Python39\lib\argparse.py", line 1821, in parse_args
    self.error(msg % ' '.join(argv))
  File "C:\Users\ubunt\AppData\Local\Programs\Python\Python39\lib\argparse.py", line 2575, in error
    self.exit(2, _('%(prog)s: error: %(message)s\n') % args)
  File "C:\Users\ubunt\AppData\Local\Programs\Python\Python39\lib\argparse.py", line 2562, in exit
    _sys.exit(status)
SystemExit: 2
←[32mINFO←[0m:     127.0.0.1:50671 - "←[1mGET /names?name=James HTTP/1.1←[0m" ←[91m500 Internal Server Error←[0m

As you can see, I want to have some default arguments and some required to be passed by the user, such as name, and I have a problem with those default parameters.

I mean, I know it's because I use in my FastAPI only one method from script (can I just run whole script?), and that's why I put ar=args() there. But it did not fix my problem.

I just want to get JSON created by create_df() method, when I just type in browser:

`api.addres.url/port/names?James` or `api.addres.url/port/name?James&?Potter`

Can someone explain me how to repair it?

Don't call out to args - instead, let your create_df function take those values as arguments, and call out to args in your __main__ method instead for the CLI version, and provide values from the web request when handling the API request. — MatsLindh
– MatsLindh, Commented Jan 20, 2022 at 12:54

Chris · Accepted Answer · 2022-10-01 15:01:00Z

3

You could do that in your endpoint instead. By not declaring a default value for the query parameter, then it automatically means that this parameter is required.

As per the documentation (have a look here as well):

When you declare a default value for non-path parameters...then it is not required.

If you don't want to add a specific value but just make it optional, set the default as None.

But when you want to make a query parameter required, you can just not declare any default value:

So, in your case, you could have something like this:

@app.get("/names")
def root(name: str, surname: str = "Smith", birthday: str = "2001"):
    print("In progress...")
    #result = create_df(name)
    return {"name": name, "surname": surname, "bd": birthday}

In your browser, you can type, for instance: 127.0.0.1:8000/names?name=James

edited Oct 1, 2022 at 15:01

answered Jan 20, 2022 at 13:02

Chris

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1 Comment

martin Over a year ago

Thank U @Chris , accodring ur advice I just change "result =..." line to: result = create_df(name=name, surname=surname, birthday=birthday)

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