#! python3
# P3_stopwatch.py - A simple stopwatch program.

import time

# Display the program's instructions
print("Press ENTER to begin. Afterwards, press ENTER to 'click' the stopwatch. "
      "Press CTRL-C to quit.")
input()  # Press Enter to begin
print('Started.')
startTime = time.time()  # Get the first lap's start time
lastTime = startTime
lapNum = 1

# Start tracking the lap times.
try:
    while True:
        input()
        lapTime = round(time.time() - lastTime, 2)
        totalTime = round(time.time() - startTime, 2)
        print("Lap #%s: %s (%s)" % (lapNum, totalTime, lapTime), end='')
        lapNum += 1
        lastTime = time.time()  # reset the last lap time
except KeyboardInterrupt:
    # Handle the CTRL-C exception to keep its error message from displaying.
    print("\nDone.")

#! python3
"""Stopwatch

A simple stopwatch program with lap times.

"""


def main():
    import time

    # Display the program's instructions
    print("Press ENTER to begin. Afterwards, press ENTER to 'click' the stopwatch. "
          "Press CTRL-C to quit.")
    input()  # Press Enter to begin
    print('Started.')
    startTime = time.time()  # Get the first lap's start time
    lastTime = startTime
    lapNum = 1

    # Start tracking the lap times.
    try:
        while True:
            input()
            lapTime = round(time.time() - lastTime, 2)
            totalTime = round(time.time() - startTime, 2)
            print("Lap #%s: %s (%s)" % (lapNum, totalTime, lapTime), end='')
            lapNum += 1
            lastTime = time.time()  # reset the last lap time
    except KeyboardInterrupt:
        # Handle the CTRL-C exception to keep its error message from displaying.
        print("\nDone.")


if __name__ == '__main__':
    main()

Update P3_stopwatch.py added docstring and wrapped in main function