http://bugs.python.org/issue4715 This patch by Antoine Pitrou optimizes the bytecode for conditional branches by merging the following "POP_TOP" instruction into the conditional jump. For example, the list comprehension "[x for x in l if not x]" produced the following bytecode: 1 0 BUILD_LIST 0 3 LOAD_FAST 0 (.0) >> 6 FOR_ITER 23 (to 32) 9 STORE_FAST 1 (x) 12 LOAD_FAST 1 (x) 15 JUMP_IF_TRUE 10 (to 28) 18 POP_TOP 19 LOAD_FAST 1 (x) 22 LIST_APPEND 2 25 JUMP_ABSOLUTE 6 >> 28 POP_TOP 29 JUMP_ABSOLUTE 6 >> 32 RETURN_VALUE but after the patch it produces the following bytecode: 1 0 BUILD_LIST 0 3 LOAD_FAST 0 (.0) >> 6 FOR_ITER 18 (to 27) 9 STORE_FAST 1 (x) 12 LOAD_FAST 1 (x) 15 POP_JUMP_IF_TRUE 6 18 LOAD_FAST 1 (x) 21 LIST_APPEND 2 24 JUMP_ABSOLUTE 6 >> 27 RETURN_VALUE Notice that not only the code is shorter, but the conditional jump (POP_JUMP_IF_TRUE) jumps right to the start of the loop instead of going through the JUMP_ABSOLUTE at the end. "continue" statements are helped similarly. Furthermore, the old jump opcodes (JUMP_IF_FALSE, JUMP_IF_TRUE) have been replaced by two new opcodes: - JUMP_IF_TRUE_OR_POP, which jumps if true and pops otherwise - JUMP_IF_FALSE_OR_POP, which jumps if false and pops otherwise

/* Cross platform case insensitive string compare functions
 */

#include "Python.h"

int
PyOS_mystrnicmp(const char *s1, const char *s2, Py_ssize_t size)
{
	if (size == 0)
		return 0;
	while ((--size > 0) &&
	       (tolower((unsigned)*s1) == tolower((unsigned)*s2))) {
		if (!*s1++ || !*s2++)
			break;
	}
	return tolower((unsigned)*s1) - tolower((unsigned)*s2);
}

int
PyOS_mystricmp(const char *s1, const char *s2)
{
	while (*s1 && (tolower((unsigned)*s1++) == tolower((unsigned)*s2++))) {
		;
	}
	return (tolower((unsigned)*s1) - tolower((unsigned)*s2));
}