dynam.py

from contextlib import contextmanager
import threading

dyn = threading.local()

@contextmanager
def dlet(**new):
    old = {}
    for name, value in new.items():
        old[name] = getattr(dyn, name, None)
        setattr(dyn, name, value)
    yield
    for name, value in old.items():
        setattr(dyn, name, value)


dyn.is_async = False
print "we call sync function, ", dyn.is_async
with dlet(is_async=True):
	print "we call async function, ", dyn.is_async
	with dlet(is_async=True):
		print "we call async function, ", dyn.is_async
		with dlet(is_async=False):
			print "we call sync function, ", dyn.is_async
		print "we call async function again, ", dyn.is_async
	print "we call async function again, ", dyn.is_async
print "we call sync function again, ", dyn.is_async