Pydantic

What is Pydantic? §

• Pydantic is a data validation library aimed to solve Python’s dynamic typing problem!
• Similar to data-classes and type hinting (which also solve dynamic typing) but more powerful

Installation,

pip install pydantic

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Pydantic vs Dataclass §

Features	Pydantic	Dataclass
Type Hints	yes	yes
Data Validation	yes	no
Serialization	yes	partial
Built-In	no	yes

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Usage §

from pydantic import BaseModel, EmailStr
 
class User(BaseModel):
	name: str
	email: EmailStr
	account_id: int
 
# Instatiation
user1 = User(
	name="nish",
	email="nish@google.com",
	account_id=1
)
 
# Instatiate from an existing object
user_data = {
	'name': 'nish',
	'email': 'nish@google.com',
	'account_id': 1
}
user2 = User(**user_data)
 
# Instantiate from a JSON string
json_str = '{"name": "nish", "email": "nish@google.com", "account_id": 1}'
user3 = User.parse_raw(json_str)

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Custom validators §

• Pydantic let’s you create custom validators using the @validator decorator
• For example say we want all account_ids to be a positive integer,

  from pydantic import BaseModel, EmailStr, validator
   
  class User(BaseModel):
  	name: str
  	email: EmailStr
  	account_id: int
   
  @validator('account_id')
  def validate_account_id(cls, value):
  	if value <= 0:
  		raise ValueError(f"account_id must be positive: {value}")
  	return value
   
  user = User(name="Nish", email="nish@gmail.com", account_id=1)
  print(user)

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Related §

Why static typing

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Refs §

1. https://www.youtube.com/watch?v=XIdQ6gO3Anc