14 posts tagged with "pydantic"

When structuring immutable, simple data in Python, developers often choose between several tools. While Dataclasses and Pydantic models dominate modern usage, older structures like namedtuple and simpler tools like tuple and dict still have niche uses.

This article compares these common data structures based on their primary function, mutability, and performance characteristics to help you choose the best tool for the job.

While both Pydantic models and Python dataclasses serve to structure data, their performance characteristics are significantly different. The key distinction lies in when and how validation occurs. Dataclasses rely on simple Python object initialization, while Pydantic executes a comprehensive validation and coercion pipeline on every instantiation.

The clear winner in terms of raw execution speed is the Python Dataclass.

The modern Python landscape offers two excellent tools for defining structured data: Dataclasses (introduced in Python 3.7) and Pydantic (a third-party library). While both help define classes for data, their core purpose, performance characteristics, and feature sets are fundamentally different.

Choosing between them depends on whether your primary need is simple data structuring (Dataclasses) or input validation and parsing (Pydantic).

📉 Drawbacks of Pydantic: A Deep Dive with Examples​

Pydantic is an indispensable tool in the modern Python ecosystem, powering frameworks like FastAPI and widely used for data validation. However, like any powerful abstraction, it comes with trade-offs. While it excels at validation and developer ergonomics, it introduces overhead and complexity that can become problematic in specific high-performance or dynamic scenarios.

This article explores the drawbacks of Pydantic, providing concrete code examples to illustrate where it might not be the best fit.

It might seem excessive to define an entire Pydantic BaseModel for a single attribute when a simple type hint like user_id: str would suffice. However, using a single-attribute Pydantic model (often called a Wrapper Model or a Value Object) offers significant advantages, primarily around reusability, centralized validation, and complex parsing.

This pattern transforms a simple type hint into a powerful, reusable validation layer.

Python annotations, introduced in PEP 3107 for function parameters and return values, were initially generic metadata slots. While their primary use has become type hinting (PEP 484), expert developers leverage them for advanced and niche applications that go far beyond simple type declarations.

These use cases often involve frameworks or metaprogramming to make annotations act as declarative configuration or runtime execution instructions.

The Wrapper Pattern (often referred to in design literature as the Decorator Pattern or Adapter Pattern when applied to classes, but used here in the broader sense of wrapping functionality or data) involves encapsulating an object or a function within another object.

In the context of Python, particularly with frameworks like FastAPI and Pydantic, the Wrapper Pattern is primarily used to:

1. Enhance or Extend Functionality without modifying the original object (Decorator/Adapter).
2. Validate and Centralize Logic for a simple data type, turning it into a Value Object (as seen with Pydantic).

Pydantic BaseModel class decorators are a powerful and modern way to customize a model's behavior and validation logic. While a lot of Pydantic's functionality is configured through class attributes or the ConfigDict, decorators offer a more explicit and code-centric approach, especially for complex validation.

Pydantic V2 introduced several new decorators to enhance validation and model configuration. The most important ones are:

• @model_validator
• @field_validator
• @computed_field

These decorators are typically imported from pydantic.

When comparing two things, the advantages are the positive aspects that make one a better choice in a given situation.

Here’s why you should choose msgspec over Pydantic.

msgspec is an extremely fast serialization and validation library that consistently outperforms Pydantic v2 in benchmarks. This performance advantage comes from its design as a lean, compiled-code-based library focused on a narrow set of data handling tasks, whereas Pydantic v2 is a feature-rich framework.

The performance differences are most pronounced in two key areas: parsing/decoding (converting data like JSON into Python objects) and serialization/encoding (converting Python objects into data like JSON).