26  Building cmd applications with typer

Typer bypasses use of sys.argv or argparse module and lets us create very powerful command line applications.

26.1 Simple example

Here is one sample application and how to pass arguments using typer module

%%file add_typer.py
import typer

def add(a: int, b: int):
    return a + b

if __name__ == "__main__":
    typer.run(add)

$ python add_typer.py --help
Usage: add_typer.py [OPTIONS] A B                                              
                                                                                
╭─ Arguments ──────────────────────────────────────────────────────────────────╮
│ *    a      INTEGER  [required]                                              │
│ *    b      INTEGER  [required]                                              │
╰──────────────────────────────────────────────────────────────────────────────╯
╭─ Options ────────────────────────────────────────────────────────────────────╮
│ --help          Show this message and exit.                                  │
╰──────────────────────────────────────────────────────────────────────────────╯

26.2 Type of argument

if you give type hints, typer will automatically detect how to convert the command line argument in given type e.g str, int etc.

%%file repeat_typer.py
import typer

def repeat(text: str, count: int):
    for i in range(count):
        print(text)

if __name__ == "__main__":
    typer.run(repeat)

!python repeat_typer.py welcome 3
welcome
welcome
welcome

26.3 Long short options

Here is one example where we can give long/short option like --base/-b

%%file dummy_typer.py
from typing import Annotated
import typer
import datetime


def dummy(target: Annotated[str, typer.Option("--target", "-t", help="Target currency")]="INR", 
          date: Annotated[str, 
              typer.Option("--date", "-d", help="Date for which data is requested")]="2023-01-31", 
          base:Annotated[str, typer.Option("--base", "-b", help="Base currency")]="USD"):
    print("You gave target as ", target)
    print("You gave date as ", date)
    print("You gave base as ", base)
    print("And this is how you can convert date to iso format")
    print(datetime.date.fromisoformat(date))
    
if __name__ == "__main__":
    typer.run(dummy)

!python dummy_typer.py --help
                                                                                
 Usage: dummy_typer.py [OPTIONS]                                                
                                                                                
╭─ Options ────────────────────────────────────────────────────────────────────╮
│ --target  -t      TEXT  Target currency [default: INR]                       │
│ --date    -d      TEXT  Date for which data is requested                     │
│                         [default: 2023-01-31]                                │
│ --base    -b      TEXT  Base currency [default: USD]                         │
│ --help                  Show this message and exit.                          │
╰──────────────────────────────────────────────────────────────────────────────╯

!python dummy_typer.py -t BITC -d "2026-01-23" -b EUR
You gave target as  BITC
You gave date as  2026-01-23
You gave base as  EUR
And this is how you can convert date to iso format
2026-01-23