Fluent Python, 2nd Edition

Chapter 5. Data Class Builders

Data classes are like children. They are okay as a starting point, but to participate as a grownup object, they need to take some responsibility.

Martin Fowler and Kent Beck¹

Python offers a few ways to build a simple class that is just a collection of fields, with little or no extra functionality. That pattern is known as a “data class”—and dataclasses is one of the packages that supports this pattern. This chapter covers three different class builders that you may use as shortcuts to write data classes:

collections.namedtuple

The simplest way—available since Python 2.6.

typing.NamedTuple

An alternative that requires type hints on the fields—since Python 3.5, with class syntax added in 3.6.

@dataclasses.dataclass

A class decorator that allows more customization than previous alternatives, adding lots of options and potential complexity—since Python 3.7.

After covering those class builders, we will discuss why Data Class is also the name of a code smell: a coding pattern that may be a symptom of poor object-oriented design.

Note

typing.TypedDict may seem like another data class builder. It uses similar syntax and is described right after typing.NamedTuple in the typing module documentation for Python 3.9.

However, TypedDict does not build concrete classes that you can instantiate. It’s just syntax to write type hints for function parameters and variables that will accept mapping values used as records, with keys as field names. We’ll see ...