For anyone else who wants to time the examples without copying & pasting each line:

    python3 -m timeit -n 1 -r 3 -s "import re ; haystack = (' ' * 20000) + 'a'" -c "re.match('\s+$', haystack)"

1 loops, best of 3: 467 usec per loop

    python3 -m timeit -n 1 -r 3 -s "import re ; haystack = (' ' * 20000) + 'a'" -c "re.search('\s+$', haystack)"

1 loops, best of 3: 4.23 sec per loop

Options

    -n  how many times to execute statement
    -r  how many times to repeat the timer
    -s  setup code (run once)
    -c  command to run n times