# We want to measure (and log) how long a chunk of code
# took to execute.
# 
# We can use time.time() function to get a timestamp right
# before and right after, and print out the difference.
#
# Implement logging the duration of the execution

from __future__ import print_function

import time
import random
import contextlib

@contextlib.contextmanager
def timeit():
    """Context manager which logs the duration of execution.

    >>> with timeit():                    # doctest: +ELLIPSIS
    ...     time.sleep(1)
    Calculations took 1...s

    >>> with timeit():                    # doctest: +ELLIPSIS
    ...     time.sleep(3)
    Calculations took 3...s
    """
    start = time.time()
    try:
        yield
    finally:
        print('Calculations took {:.2g}s'.format(time.time() - start))

def long_haul(*args):
    "Uses time.sleep() to simulate long calculations"
    time.sleep(5 * random.random())
    return sum(args)

if __name__ == '__main__':
    print('Will do calculations now')
    with timeit():
        ans = long_haul(1, 2, 3)
    print(ans)

# Please note:
# We could do it also in the traditional way
# using something like:
#
#   print('Will do calculations now')
#   start = time.time()
#   ans = long_haul()
#   duration = time.time() - start
#   print('Calculations took {}s'.format(duration))
#
# but this is harder to read, and leaves the
# 'start' and 'duration' names in the local scope.
#
# To test this file, use:
#  py.test-3.4 --doctest-modules cm_timer.py -v
# or
#  python3 -m doctest cm_timer.py