I've found strange performance issue when using default value, the
test code is list below:
from timeit import Timer
def f(x):
y = x
y.append(1)
return y
def g(x=[]):
y = []
y.append(1)
return y
def h(x=[]):
y = x
y.append(1)
return y
def f2(x):
y = x
y.append(1)
return y + []
def g2(x=[]):
y = []
y.append(1)
return y + []
def h2(x=[]):
y = x
y.append(1)
return y + []
TIMES = 10000
print Timer('f([])','from __main__ import f, g, h').timeit(TIMES)
print Timer('g()','from __main__ import f, g, h').timeit(TIMES)
print Timer('h([])','from __main__ import f, g, h').timeit(TIMES)
print Timer('h()','from __main__ import f, g, h').timeit(TIMES)
print Timer('f2([])','from __main__ import f2, g2, h2').timeit(TIMES)
print Timer('g2()','from __main__ import f2, g2, h2').timeit(TIMES)
print Timer('h2([])','from __main__ import f2, g2, h2').timeit(TIMES)
print Timer('h2()','from __main__ import f2, g2, h2').timeit(TIMES)
I tested it with Python 2.5.4, 2.6.4 and 3.1.1 on Windows XP, and get
almost the same result:
0.00449247041174
0.00439608944712
0.00455867994396
0.00327471787615
0.00791581052899
0.00684919452053
0.00734311204357
0.30974942346
h2() is about 42 times slower than h2([]), but h() is a litter faster
than h([]).
If change TIMES to 20000, other results are 2 times than before, but h2
() is 4 times(about 1.2 sec) than before.
Is there any tricks in it?
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