iife

Immediately-invoked function expressions in Python

The iife package provides a decorator function iife that calls the function/class it decorates and assigns the result to the name of the function/class.

Some use cases include...

Creating an anonymous object.

Have you ever written a class that you know will only have one instance? You can use the iife decorator to create that instance immediately.

from iife import iife

@iife
@dataclass
class player:
    x: int = 1
    y: int = 2

# player is an instance of the player class
player.x # -> 1

# The class cannot be reinstantiated because the name is shadowed.
new_player = player(x=3, y=4) # -> SyntaxError

This might also be useful in library development to hide the implementation details of the class from the end user, who can only access the single instance.

Complex initialization.

Sometimes a variable needs to be initialized by complex logic that cannot be expressed as a single assignment. Traditionally, this can be done with temporarily setting the variable to a default value:

x = None
y = [1, 2, 3]
for i in y:
    if i == 2:
        x = i

Why not do it with an IIFE? (To be honest, this isn't the best example, but it's more fun to do it like this.)

from iife import iife

@iife
def x() -> Optional[int]:
    y = [1, 2, 3]
    for i in y:
        if i == 2:
            return i

... And a bunch more. Maybe. Tbh this is mostly for fun.