BaseModel
- Python course
- Advanced
- Lesson 55/83
- 5 min
Learn to define models with pydantic.BaseModel.
BaseModel
pydantic.BaseModel is the base class for data models. You derive a class, give types to fields; Pydantic validates the data and converts it automatically.
from pydantic import BaseModel
class User(BaseModel):
name: str
age: int
u = User(name="Ayşe", age=30)
print(u.name, u.age) # Ayşe 30Wrong types raise a Pydantic error. You can also build a model from a dict; a missing field still raises an error.
Fields and types
Each field is defined with a type: str, int, float, bool, list and so on. Pydantic tries to convert data to this type; if it cannot, it raises.
class User(BaseModel):
name: str
age: int
active: bool
u = User(name="Ayşe", age="30", active=True)
print(u.age) # 30 (converted to int)This is useful when the data source is untrusted; for example, strings from a form are turned into integers automatically.
Practice Create a User model
Start with from pydantic import BaseModel. Define class User(BaseModel): with fields name: str and age: int. Create an instance with u = User(name="Ayşe", age=30). Print the values with print(u.name, u.age).
Starter code
# bring in BaseModel from pydantic
# define User class (derive from BaseModel, name and age fields)
# create a User instance (Ayşe, 30)
# print the name and age valuesSample solution
from pydantic import BaseModel
class User(BaseModel):
name: str
age: int
u = User(name="Ayşe", age=30)
print(u.name, u.age)Expected output
Ayşe 30
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What happens if you omit a field in a model derived from BaseModel?
- The field becomes None
- An error is raised Correct answer
- The field becomes an empty string
- A warning is issued but it continues
Explanation: A missing required field raises a Pydantic error.
2 Complete the BaseModel derivation
from pydantic import BaseModel
class User(____):
name: str
age: intfrom pydantic import BaseModel
class User(BaseModel):
name: str
age: intExplanation: class User(BaseModel) defines a model.
3 Match the BaseModel concepts
| Term | Meaning |
|---|---|
BaseModel |
Is the base class |
name: str |
Is a field definition |
User(name=, age=) |
Creates an instance |
u.name |
Is the field value |