from time import time, sleep
from functools import wraps

class TimeMeasurer:
    """Decorator to print time elapsed to execute some function"""
    def __call__(self, function_to_measure):
        @wraps(function_to_measure)
        def measurer_wrapper():
            start_time = time()
            value = function_to_measure()
            elapsed = time() - start_time
            print('Execution time: {}s'.format(elapsed))
            return value

        return measurer_wrapper


@TimeMeasurer()
def some_complex_function():
    print('Lets begin...')
    sleep(2.3)
    print('I\'m done!')

some_complex_function()