How to dynamically load a Python class

python

dynamic-import

importlib

python-best-practices

byNikita Barsukov·Sep 25, 2024

Want to dynamically load a class in Python? Use __import__() for module loading and getattr() to extract the class. Try this:

module = __import__('module_name', globals(), locals(), ['object'], -1)
MyClass = getattr(module, 'ClassName')
instance = MyClass()

This code instantly loads ClassName from our module_name.py file. To create an instance use instance = MyClass().

Safer and cleaner: importlib

While __import__() is great, the importlib library often offers cleaner syntax:

import importlib

module = importlib.import_module('module_name')
MyClass = getattr(module, 'ClassName')
instance = MyClass()

No rocket science, right?

Loading a class from a module path

For fully-qualified class names, split on the last dot to separate the module name and class name:

def my_import(name):
    """ Walks the walk, talks the talk, does the 'dynamic import' rock! """
    module, _, cls = name.rpartition('.')
    mod = __import__(module, fromlist=[cls])
    return getattr(mod, cls)

MyClass = my_import('package.module.ClassName')
instance = MyClass()  # Performs inception. Not affiliated with Leonardo DiCaprio.

The importance of `fromlist`

As the old programmer proverb goes, "If thou forgets fromlist, thy code shall be forgetten". Ensure non-empty fromlist especially when you're on Google App Engine, which is a bit fussy.

module = __import__('module_name', fromlist=['ClassName'])

Failing gracefully

No class should go missing on your watch. If a module or class can't be found, consider using Python's error handling capabilities:

try {
    MyClass = my_import('my_never_seen_before_class')
} except ImportError as e:
    print(f'Something bad happened during import, but we got it covered: {e}')