What is it actually doing here? A 3ghz cpu has 3 billion cycles per second. So it's spending an average of 44 cycles to increment an integer and compare???
(also fun fact, python integers are 28 bytes, but it still doesn't really explain the slowness: `import sys; sys.getsizeof(123456)`)
(That's after subtracting about 30 million cycles of startup overhead. Tested with Python 2.7.9 on an Intel i3-4160 processor.)
Remember, Python is a bytecode-interpreted language. Each iteration of the loop involves multiple bytecode operations:
2 0 SETUP_LOOP 20 (to 23)
3 LOAD_GLOBAL 0 (xrange)
6 LOAD_FAST 0 (NUMBER)
9 CALL_FUNCTION 1
12 GET_ITER
>> 13 FOR_ITER 6 (to 22)
16 STORE_FAST 1 (_)
3 19 JUMP_ABSOLUTE 13
>> 22 POP_BLOCK
>> 23 LOAD_CONST 0 (None)
26 RETURN_VALUE
Frankly, it's impressive that it's as fast as it is.
Oof.
My understanding was that to access a variable, python does a dictionary lookup to match the name to a memory location, which would explain what happens with an older python.
(Personally, I really question the extremely-dynamic-by-default design of that generation of languages; is being able to treat globals as a dictionary occasionally worth forcing a key lookup on every single global use?)