On 05/05/2015 04:30 PM, Ian Kelly wrote:
On Tue, May 5, 2015 at 12:45 PM, Dave Angel <da...@davea.name> wrote:
When the "simple" is True, the function takes noticeably and consistently
longer. For example, it might take 116 instead of 109 seconds. For the
same counts, your code took 111.
I can't replicate this. What version of Python is it, and what value
of x are you testing with?
I've looked at dis.dis(factorial_iterative), and can see no explicit reason
for the difference.
My first thought is that maybe it's a result of the branch. Have you
tried swapping the branches, or reimplementing as separate functions
and comparing?
Logic is quite simple:
def factorial_iterative(x, simple=False):
assert x >= 0
result = 1
j=2
if not simple:
for i in range(2, x + 1):
#print("range value is of type", type(i), "and value", i)
#print("ordinary value is of type", type(j), "and value", j)
result *= i
j += 1
else:
for i in range(2, x + 1):
result *= j
j += 1
return result
def loop(func, funcname, arg):
start = time.time()
for i in range(repeats):
func(arg, True)
print("{0}({1}) took {2:7.4}".format(funcname, arg, time.time()-start))
start = time.time()
for i in range(repeats):
func(arg)
print("{0}({1}) took {2:7.4}".format(funcname, arg, time.time()-start))
repeats = 1
and arg is 10**4
loop(factorial_iterative, "factorial_iterative ", arg)
My actual program does the same thing with other versions of the
function, including Cecil's factorial_tail_recursion, and my optimized
version of that.
Python 3.4.0 (default, Apr 11 2014, 13:05:11)
[GCC 4.8.2] on linux
factorial_iterative (100000) took 3.807
factorial_iterative (100000) took 3.664
factorial_iterative (200000) took 17.07
factorial_iterative (200000) took 15.3
factorial_iterative (300000) took 38.93
factorial_iterative (300000) took 36.01
Note that I test them in the opposite order of where they appear in the
function. That's because I was originally using the simple flag to test
an empty loop. The empty loop is much quicker either way, so it's not
the issue. (But if it were, the for-range version is much quicker).
I think I'll take your last suggestion and write separate functions.
--
DaveA
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