# custom_timestamp.py
from time import sleep


def debug(*msg, timestamp=[None]):
    print(*msg)
    from time import time  # local import
    if timestamp[0] is None:
        timestamp[0] = time()  #1
    else:
        now = time()
        print(
            ' Time elapsed: {:.3f}s'.format(now - timestamp[0])
        )
        timestamp[0] = now  #2


debug('Entering nasty piece of code...')
sleep(.3)
debug('First step done.')
sleep(.5)
debug('Second step done.')


"""
$ python custom_timestamp.py
Entering nasty piece of code...
First step done.
 Time elapsed: 0.300s
Second step done.
 Time elapsed: 0.500s
"""