first demo

main.py

@@ -1,6 +1,30 @@
+# example from root.cz
+# https://www.root.cz/clanky/validace-dat-v-pythonu-s-vyuzitim-knihovny-pydantic/
+
+from models.User import User, UserNone, UserUnion, UserPositiveInt, UserFieldValidator, UserMaxLength
+
+
 def main():
     print("Hello from pydantic-demo!")
+    print(f"{User(name="John", surname="Doe", age=42, registered=True)=}")
+    print(f"{User(name="Adam", surname="Bernau", age=52, registered=True)=}")
+    print(f"{UserNone(name="Adam", surname="Bernau", age=None)=}")
+    print(f"{UserUnion(name="Adam", surname="Bernau", age=None)=}")
+    print(f"{UserUnion(name="Adam", surname="Bernau")=}")
+    print(f"{UserPositiveInt(name="Adam", surname="Bernau")=}")
+    #print(f"{UserPositiveInt(name="Adam", surname="Bernau", age=-50)=}")
+    print(f"{UserFieldValidator(name="Adam", surname="Bernau", age=18)=}")
+    print(f"{UserMaxLength(name="Adam", surname="Bernau", age=18)=}")
+    #print(f"{UserMaxLength(name="Adam", surname="Bernaukjghsmtlmgchs", age=18)=}")
 
+    # JSON
+    data = """
+        {"name": "John",
+         "surname": "Doe",
+         "age": 18
+        }
+    """
+    print(f"{UserMaxLength.model_validate_json(data)=}")
 
 if __name__ == "__main__":
     main()

models/User.py

@@ -0,0 +1,61 @@
+from __future__ import annotations
+
+from typing import Union, Optional
+from pydantic import BaseModel, PositiveInt, field_validator, Field
+
+
+class User(BaseModel):
+    name: str
+    surname: str
+    age: int
+    registered: bool
+
+class UserNone(BaseModel):
+    # preferred variant
+    name: str
+    surname: str
+    age: int | None
+    registered: bool = False
+
+class UserUnion(BaseModel):
+    name: str
+    surname: str
+    age: Union[int, None] = None
+    registered: bool = False
+
+class UserOptional(BaseModel):
+    name: str
+    surname: str
+    age: Optional[int] # default value is None
+    registered: bool = False
+
+class UserPositiveInt(BaseModel):
+    name: str
+    surname: str
+    age: Union[PositiveInt, None] = None
+    registered: bool = False
+
+class UserFieldValidator(BaseModel):
+    name: str
+    surname: str
+    age: PositiveInt | None
+    registered: bool = False
+
+    @field_validator("age")
+    def validate_age(cls, value):
+        if value < 18:
+            raise ValueError("age must be at least 18")
+        return value
+
+
+class UserMaxLength(BaseModel):
+    name: str = Field(..., max_length=10)
+    surname: str = Field(..., max_length=10)
+    age: PositiveInt | None
+    registered: bool = False
+
+    @field_validator("age")
+    def check_age(cls, value):
+        if value < 18:
+            raise ValueError("You are too young to register")
+        return value