[peachy_no_pie]

What about:

    def foo(Bar=Bar):
        bar = Bar()
        ...

Pass in the class or any callable and then call it in the body to make an instance.

[dragonwriter]

The problem with that compared to late-bound parameters is that you have to pass it a callable for non-default uses as well. It's nice sometimes to have a deferred (callable-supplied) default but pass immediate values for non-default.

[ShamelessC]

Yeah, this is the correct answer and it works with functions or objects.

This is commonly used to implement logging callbacks e.g.

    from collections.abc import Callable
    
    def log_fn(message: str = ''):
        print(f'This is your log: {message}')
    
    def run_read_file(file_to_read:str, log_handler: Callable=log_fn):
        contents = open(file_to_read).readlines()
        for line in contents:
            log_handler(message=line)