Question

My programming fundamentals teacher had said in one of her classes that using the “break” or “continue” keywords is less efficient then using a boolean to exit a loop.

I wrote and ran a program written in Python to see if this was the case:

import time;

TIMES = 100000000
COMPARE_FROM = "foo"
COMPARE_TO = "roo"

def breakTest() :
    while(True) :
        break;
        if(COMPARE_FROM == COMPARE_TO) :
            boo = "boo"

def booleanTest() :
    running = True;
    while(running) :
        running = False;
        if(running):
            if(COMPARE_FROM == COMPARE_TO) :
                boo = "boo"

def main() :
    breakTimeBefore = 0;
    breakTimeAfter = 0;
    booleanTimeBefore = 0;
    booleanTimeAfter = 0;

    print("running break test ...");

    breakTimeBefore = time.time();
    for i in range(0, TIMES, 1):
        breakTest();
    breakTimeAfter = time.time();

    print("break test complete");
    print("Time: %f seconds \n" % (breakTimeAfter - breakTimeBefore));

    print("running boolean test ...");

    booleanTimeBefore = time.time();
    for i in range(0, TIMES, 1):
        booleanTest();
    booleanTimeAfter = time.time();

    print("boolean test complete");
    print("Time: %f seconds \n" % (booleanTimeAfter - booleanTimeBefore))

    print("---- FINDINGS ----");
    print("breakTest time:   %f" % (breakTimeAfter - breakTimeBefore));
    print("booleanTest time: %f" % (booleanTimeAfter - booleanTimeBefore));
    print("diffrence:        %f" % ((breakTimeAfter - breakTimeBefore) - (booleanTimeAfter - booleanTimeBefore)));
    input("Press enter to close...");

main();

After running it three times, and averaging the results, i found that the breakTest was 6.25 seconds faster.

So is the break keyword more efficient or is my code wrong?

Answer 1

Your tests are not exactly equivalent. I think your teacher may have had something more like the following in mind:

def breakTest():
    i = 0
    while True:
        i += 1
        if i == 10:
            break

def booleanTest():
    i = 0
    while i < 10:
        i += 1

As you can see below, putting the condition into the while statement instead of having an if/break does improve performance (and shorten code):

In [14]: %timeit breakTest()
1000000 loops, best of 3: 999 ns per loop

In [15]: %timeit booleanTest()
1000000 loops, best of 3: 201 ns per loop

Note that this is just an example of the different ways to exit the loop and what I think your teacher meant. Of course if you were actually writing this code, you should use for i in range(11): ...