context.py

import time
from contextlib import contextmanager

@contextmanager
def timed(metric, tags=None):
    start = time.time()
    try:
        yield tags
    finally:
        print tags
        dt = (time.time() - start) * 1000.0
        print dt


def main():
    with timed('asdf', tags={'asdf': 'qwer'}) as yolo:
        yolo['qqq'] = 'aaa'
        time.sleep(1)


if __name__ == '__main__':
    main()