Python enter_context

enter_context.py

"""Imperative enter/exit control for python contextmanagers.

Where you'd prefer to use `with`:

    with my_context(123) as f:
        do_something()

but only have access to before and after hook-functions (as with Flask):

    def before_hook():
        pass  # Enter the context.
    def after_hook():
        pass  # Exit the context.

    def handler():
        return do_something()

you can use the `enter_context` function as an open/close pair of functions:

    ctxt = threading.local()

    def before_hook():
        f, ctxt.close_context = enter_context(my_context, 123)
    def after_hook():
        ctxt.close_context()

    def handler():
        return do_something()
"""
from contextlib import contextmanager
from functools import partial


def main():
    with context(123) as mgr:
        print "middle: %r" % (mgr,)

    print "---"

    mgr, exit_context = enter_context(context, 456)
    print "middle: %r" % (mgr,)
    exit_context()


@contextmanager
def context(*args, **kwargs):
    print "in"
    yield {'args': args, 'kwargs': kwargs}
    print "out"


def enter_context(func, *args, **kwargs):
    def enter():
        with func(*args, **kwargs) as f:
            yield f
    e = enter()
    def exit():
        try:
            next(e)
        except StopIteration:
            pass
    return next(e), exit


if __name__ == "__main__":
    main()

$ python context_faker.py
in
middle: {'args': (123,), 'kwargs': {}}
out

---
in
middle: {'args': (456,), 'kwargs': {}}
out