Why is my Python code faster than my C code?

Question

I recently began learning C, so as a performance test versus python I created the following code to loop through every possible 8 character alphanumeric combination. I noticed the python code ran roughly 20x faster than the C code despite the fact they were mostly the same code. I used PyCharm for the python code and CLion for the C code. Running the .exe file outside of CLion produced the same speed. Here is the code.

Python:

char_list = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u',
             'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9']

for char1 in char_list:
    for char2 in char_list:
        for char3 in char_list:
            for char4 in char_list:
                for char5 in char_list:
                    for char6 in char_list:
                        for char7 in char_list:
                            for char8 in char_list:
                                print(char1 + char2 + char3 + char4 + char5 + char6 + char7 + char8)

C:

#include <stdio.h>

int main() {
    char charset[] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
                      't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};

    for (int i1 = 0; i1 < sizeof charset; i1++) {
        for (int i2 = 0; i2 < sizeof charset; i2++) {
            for (int i3 = 0; i3 < sizeof charset; i3++) {
                for (int i4 = 0; i4 < sizeof charset; i4++) {
                    for (int i5 = 0; i5 < sizeof charset; i5++) {
                        for (int i6 = 0; i6 < sizeof charset; i6++) {
                            for (int i7 = 0; i7 < sizeof charset; i7++) {
                                for (int i8 = 0; i8 < sizeof charset; i8++) {
                                    printf("%c%c%c%c%c%c%c%c\n", charset[i1], charset[i2], charset[i3], charset[i4],
                                           charset[i5], charset[i6], charset[i7], charset[i8]);
                                }
                            }
                        }
                    }
                }
            }
        }
    }

    return 0;
}

Comments are not for extended discussion; this conversation has been moved to chat. — Samuel Liew
– Samuel Liew, Commented Feb 20, 2022 at 15:05

Pychopath · Accepted Answer · 2022-02-19 08:05:50Z

2

Tried it myself, in a console, measuring the time for the first ten million lines:

Python:

$ time python3 main.py | head -10000000 | tail
...
real    0m6.075s
user    0m6.246s
sys     0m0.262s

C, compiled both ways mentioned in the first answer (now deleted):

$ gcc main.c -o main
$ time ./main | head -10000000 | tail
...
real    0m2.140s
user    0m2.350s
sys     0m0.300s

$ gcc -O3 -Ofast -Og -Os -funroll-loops -s main.c -o main
$ time ./main | head -10000000 | tail
...
real    0m2.119s
user    0m2.278s
sys     0m0.347s

My conclusion: Python isn't 20x faster at this but is slower, and what you observed is rather a slow speed of the consoles in which you ran the C program.

edited Feb 19, 2022 at 8:05

answered Feb 19, 2022 at 7:20

Pychopath

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13 Comments

joshdimatteo Over a year ago

That makes a lot of sense. I know the issue lies in the method of printing to the consoles because after experimenting without using printing, I found C to be much faster. I'd still like to figure out a way to make printing to the console faster in C. I'll be doing a ton of research on optimization probably.

Jabberwocky Over a year ago

@jmd123 don't waste your time trying to make console output faster, it's pointless to have faster console output anyway. The speed here is essentially determined by the speed the console processes output.

Jabberwocky Over a year ago

@jmd123 what's the point of having fast console output anyway? Are you going to stare at the console while the program is running? What problem are you actually trying to solve?

Pychopath Over a year ago

@jmd123 Probably the way to make your C program print to the console faster is ... use a faster console. And if you just want to keep an eye on the program's progress, print every millionth line or so.

Pychopath Over a year ago

@Clifford Meh, I already shut the GCE instance down, and it doesn't matter for the point of the question/answer anyway, so I'll probably just keep it as it is. But thanks.

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