What does __all__ mean in Python

Python __all__ is a list of public objects of that module, as interpreted by import *. The __all__  overrides the default of hiding everything that begins with an underscore. 

Python __all__ is a variable that can be set in the __init__.py file of a package. The __all__ variable is a list of strings that defines symbols imported when a program does.

Objects that start with an underscore or are not mentioned in __all__ if __all__ is present are not precisely hidden; they can be seen and accessed ideally if you know their names.

The __all__ in Python is a list of strings defining what symbols in a module will be exported when from <module> import * is used on the module.

The __all__ tells the module’s semantically “public” names. If there is a name in __all__, the users are expected to use it, and they can expect that it will not change.

Python will default export all names that do not start with an _. So you certainly could rely on this mechanism.

Using the _ convention can be more elegant because it removes the redundancy of naming the names again.

It’s worth noting that while the __all__ attribute provides a convenient way to control what is exported when using the from module import * syntax, it’s generally considered better practice to use explicit imports rather than wildcard imports, as they make it clearer what names are being used in the code.

Example

The following file data.py explicitly exports the variables men and lifestyle.

__all__ = ['men', 'lifestyle']

men = 5

def lifestyle(): return 'lifestyle'

These variables can then be imported in an app.py file like the following.

from data import *

print(men)

print(lifestyle())

Output

5

lifestyle

So, if you comment the __all__ = [‘men’, ‘lifestyle’], then the code will be executed to completion, as the default behavior of import * is to import all variables that do not begin with the underscore, from the given namespace.

The __all__ in __init__.py

The __init__.py files are required to make Python treat the directories as containing packages.

In the simplest case, __init__.py can be an empty file, but it can also execute the initialization code for the package or set the __all__ variable.

A package is typically made up of modules that may import one another but are necessarily tied together with an __init__.py file.

That’s it.