Python for loop performance in global space vs inside a function

Asked Jul 16 '15 at 02:11

Active Jul 16 '15 at 07:10

Viewed 109 times

I've been trying to understand Python for loop performance, here I found that for loop with same iterations in global space is taking much time compared with one inside a function.

import time

MAX_NUM = 50000000

# Running for loop in global space
start = time.time()

for i in xrange(MAX_NUM):
    pass

print time.time() - start


# Running th same kind of loop within a function
def foo():
    for i in xrange(MAX_NUM):
        pass

start = time.time()
foo()
print time.time() - start

When I execute this I've witnessed a huge difference in execution times.

2.00527501106
0.811304092407

I'm wondering that what makes this huge difference in execution time? how for loop performance affects from global space to write inside a function?

asked Jul 16 '15 at 02:11

gsb-eng

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Have you tried looking at the disassembled bytecode? – Barmar Jul 16 '15 at 02:15
this is really just a guess, but i think python might know that foo doesn't actually do anything so i can just skip it, while it has to run the global stuff. – Neil Locketz Jul 16 '15 at 02:15
1

This may help: http://stackoverflow.com/questions/11241523/why-does-python-code-run-faster-in-a-function – YS-L Jul 16 '15 at 02:16
@NeilLocketz If that's true, `0.8` is an awfully long time to do nothing. – Barmar Jul 16 '15 at 02:16
@Barmar, this is true. Also why i said its a guess xD – Neil Locketz Jul 16 '15 at 02:17
@Barmer : Not yet, but I've been going through Python source code to find how different name spaces affects performance. – gsb-eng Jul 16 '15 at 02:20

Python for loop performance in global space vs inside a function

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