Python's __all__: Packages, Modules, and Wildcard Imports

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March 04, 2024
Python's __all__: Packages, Modules, and Wildcard Imports
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Python has something called wildcard imports, which look like from module import *. This type of import allows you to quickly get all the objects from a module into your namespace. However, using this import on a package can be confusing because it’s not clear what you want to import: subpackages, modules, objects? Python has the __all__ variable to work around this issue.

The __all__ variable is a list of strings where each string represents the name of a variable, function, class, or module that you want to expose to wildcard imports.

In this tutorial, you’ll:

  • Understand wildcard imports in Python
  • Use __all__ to control the modules that you expose to wildcard imports
  • Control the names that you expose in modules and packages
  • Explore other use cases of the __all__ variable
  • Learn some benefits and best practices of using __all__

To get the most out of this tutorial, you should be familiar with a few Python concepts, including modules and packages, and the import system.

Importing Objects in Python

When creating a Python project or application, you’ll need a way to access code from the standard library or third-party libraries. You’ll also need to access your own code from the multiple files that may make up your project. Python’s import system is the mechanism that allows you to do this.

The import system lets you get objects in different ways. You can use:

  • Explicit imports
  • Wildcard imports

In the following sections, you’ll learn the basics of both strategies. You’ll learn about the different syntax that you can use in each case and the result of running an import statement.

Explicit Imports

In Python, when you need to get a specific object from a module or a particular module from a package, you can use an explicit import statement. This type of statement allows you to bring the target object to your current namespace so that you can use the object in your code.

To import a module by its name, you can use the following syntax:

Python 
import module [as name]

This statement allows you to import a module by its name. The module must be listed in Python’s import path, which is a list of locations where the path based finder searches when you run an import.

The part of the syntax that’s enclosed in square brackets is optional and allows you to create an alias of the imported name. This practice can help you avoid name collisions in your code.

As an example, say that you have the following module:

Python calculations.py 
def add(a, b):
    return float(a + b)

def subtract(a, b):
    return float(a - b)

def multiply(a, b):
    return float(a * b)

def divide(a, b):
    return float(a / b)

This sample module provides functions that allow you to perform basic calculations. The containing module is called calculations.py. To import this module and use the functions in your code, go ahead and start a REPL session in the same directory where you saved the file.

Then run the following code:

Python 
>>> import calculations

>>> calculations.add(2, 4)
6.0
>>> calculations.subtract(8, 4)
4.0
>>> calculations.multiply(5, 2)
10.0
>>> calculations.divide(12, 2)
6.0

The import statement at the beginning of this code snippet brings the module name to your current namespace. To use the functions or any other object from calculations, you need to use fully qualified names with the dot notation.

You can also use a similar syntax to import a Python package:

Read the full article at https://realpython.com/python-all-attribute/ »

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March 04, 2024 at 07:30PM
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