Example of prebound method pattern (https://python-patterns.guide/python/prebound-methods/) using lazily loaded global instance

__init__.py

from functools import partial

_implementation = None

def _determine_filename():
    # logic to decide on a filename for an underlying resource, or None
    ...

def load_implementation(filename=None):
    # logic to find an implementation, either returning it or raising an exception
    if filename is None:
        filename = _determine_filename()
    if filename is None:
        # adjust exception as appropriate
        raise RuntimeError("implementation could not be found")
    ...

# meta magic to generate wrappers for methods of the lazily loaded implementation.
def _wrapper(attrname, *args, implementation_src=None, **kwargs):
    if _implementation is None:
        _implementation = load_implementation(implementation_src)
    elif implementation_src is not None:
        ... # could raise an exception, or replace the implementation, or ignore it
    return getattr(_implementation, attrname)(*args, **kwargs)
    
# example of exposing a method
example_action = partial(_wrapper, 'example_action')