Traitlets: Python Configuration System

5.14.3 · active · verified Sat Mar 28

Traitlets is a Python library that provides a framework for defining attributes with type checking, dynamic default values, and change callbacks. It is currently at version 5.14.3, released on April 19, 2024, and follows a regular release cadence with periodic updates and maintenance improvements.

Warnings

breaking Traitlets 5.0 removed support for Python 2 and versions 3.0-3.6, now requiring Python 3.7 or higher.
Fix: Upgrade your Python environment to version 3.7 or higher.
deprecated The 'six' library is no longer a dependency as of Traitlets 5.0.0.
Fix: Ensure your code does not rely on 'six' for compatibility between Python 2 and 3.
gotcha Using 'default' as a method name without the '@default' decorator will not set the default value for the trait.
Fix: Decorate the method with '@default('trait_name')' to set the default value.

Install

pip install traitlets Install Traitlets

Imports

HasTraits
```
from traitlets import HasTraits
```
Correct import path for defining classes with trait attributes.
Unicode
```
from traitlets import Unicode
```
Correct import path for defining Unicode trait attributes.
Int
```
from traitlets import Int
```
Correct import path for defining Integer trait attributes.
default
```
from traitlets import default
```
Correct import path for defining default values for traits.

Quickstart

A simple example demonstrating the use of Traitlets to define a class with a 'username' attribute that defaults to the current system user.

import getpass
from traitlets import HasTraits, Unicode, default

class Identity(HasTraits):
    username = Unicode()

    @default('username')
    def _default_username(self):
        return getpass.getuser()

identity = Identity()
print(identity.username)

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