Argument parser from a Pydantic model

Question

How do I create an argument parser (argparse.ArgumentParser) from a Pydantic model?

I have a Pydantic model:

from pydantic import BaseModel, Field

class MyItem(BaseModel):
    name: str
    age: int
    color: str = Field(default="red", description="Color of the item")

And I want to create an instance of MyItem using command line:

python myscript.py --name Jack --age 10 --color blue

This should yield to:

item = MyItem(name="Jack", age=10, color="blue")
... # Process the item

I would not like to hard-code the command-line arguments and I would like to create the command-line arguments dynamically from the Pydantic model.

score 9 · Accepted Answer · answered Jun 24 '22 at 09:10

I found an answer myself. Just:

create an argument parser,
turn the fields of the model as arguments of the parser,
parse the command-line arguments,
turn the arguments as dict and pass them to the model and
process the instance of the model

import argparse
from pydantic import BaseModel, Field

class MyItem(BaseModel):
    name: str
    age: int
    color: str = Field(default="red", description="Color of the item")

def add_model(parser, model):
    "Add Pydantic model to an ArgumentParser"
    fields = model.__fields__
    for name, field in fields.items():
        parser.add_argument(
            f"--{name}", 
            dest=name, 
            type=field.type_, 
            default=field.default,
            help=field.field_info.description,
        )

# 1. Create and parse command line arguments
parser = argparse.ArgumentParser()

# 2. Turn the fields of the model as arguments of the parser
add_model(parser, MyItem)

# 3. Parse the command-line arguments
args = parser.parse_args()

# 4. Turn the arguments as dict and pass them to the model
item = MyItem(**vars(args))

# 5. Do whatever
print(repr(item))
...

You may also add subparsers if you wish to add more functionality to the parser: https://docs.python.org/3/library/argparse.html#argparse.ArgumentParser.add_subparsers

Argument parser from a Pydantic model

1 Answers1