pydantic example

pydantic_example.py

# /// script
# requires-python = "==3.12.*"
# dependencies = ["pydantic==2.10.*"]
# ///

"""
Pydantic example
- Pydantic is a data validation package for Python. Using rust, it's fast.
- <https://docs.pydantic.dev/latest/>

Usage:
    uv run ./pydantic_example.py

See output at bottom.
"""

import pprint
from datetime import datetime

from pydantic import BaseModel, Field, ValidationError


class User(BaseModel):
    username: str
    age: int = Field(..., gt=0, lt=120)  # age must be between 1 and 119
    email: str
    signup_ts: datetime | None = None


## valid example --------------------------------
user1 = User(username='john_doe', age=30, email='[email protected]')
print('')
print('all good...')
print(user1.username)
print('---\n')

## invalid example ------------------------------``
try:
    user2 = User(username='john2_doe2', age=200)
except ValidationError as e:
    print('human-readable errors...')
    print(e)
    print('---\n')

    print('errors as list of dicts...')
    errors: list = e.errors()
    print(pprint.pformat(errors, indent=2, sort_dicts=False))
    print('---\n')

    print('errors as json...')
    errors_json: list = e.json(indent=2)
    print(errors_json)
    print('---\n')


"""
Outuput...

% uv run ./pydantic_example.py

all good...
john_doe
---

human-readable errors...
2 validation errors for User
age
  Input should be less than 120 [type=less_than, input_value=200, input_type=int]
    For further information visit https://errors.pydantic.dev/2.10/v/less_than
email
  Field required [type=missing, input_value={'username': 'john2_doe2', 'age': 200}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.10/v/missing
---

errors as list of dicts...
[ { 'type': 'less_than',
    'loc': ('age',),
    'msg': 'Input should be less than 120',
    'input': 200,
    'ctx': {'lt': 120},
    'url': 'https://errors.pydantic.dev/2.10/v/less_than'},
  { 'type': 'missing',
    'loc': ('email',),
    'msg': 'Field required',
    'input': {'username': 'john2_doe2', 'age': 200},
    'url': 'https://errors.pydantic.dev/2.10/v/missing'}]
---

errors as json...
[
  {
    "type": "less_than",
    "loc": [
      "age"
    ],
    "msg": "Input should be less than 120",
    "input": 200,
    "ctx": {
      "lt": 120
    },
    "url": "https://errors.pydantic.dev/2.10/v/less_than"
  },
  {
    "type": "missing",
    "loc": [
      "email"
    ],
    "msg": "Field required",
    "input": {
      "username": "john2_doe2",
      "age": 200
    },
    "url": "https://errors.pydantic.dev/2.10/v/missing"
  }
]
---
"""