Field constraints in Python

Field carries the bounds, so validation lives with the declaration.

from pydantic import BaseModel, Field, ValidationError


class Step(BaseModel):
    title: str = Field(max_length=60)
    stars: int = Field(default=0, ge=0, le=3)
    target_tpm: int = Field(alias="tpm3", gt=0, description="3-star bar")


step = Step(title="Slices", stars=2, tpm3=95)
print(step.stars, step.target_tpm)

try:
    Step(title="x", stars=9, tpm3=95)
except ValidationError as exc:
    print(exc.errors()[0]["msg"])

How it works

ge, le and max_length are checked before your code runs.
alias maps an incoming key to a different attribute name.
description and examples end up in the generated schema.

Keywords and builtins used here

Step
as
class
except
int
print
str
try

The run, in numbers

Lines: 16
Characters to type: 409
Tokens: 131
Three-star pace: 105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 75 seconds.

Type this snippet

Step 2 of 5 in Pydantic models, step 2 of 19 in Web services & data access.

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