Fredrik Lundh wrote:
> George Sakkis wrote:
>
>> It shouldn't come as a surprise if it turns out to be slower, since
>> the nested function is redefined every time the outer is called.
>
> except that it isn't, really: all that happens is that a new function
> object is created from prebuilt parts, and assigned to a local
> variable. it's not slower than, say, a method call.
>
It looks to be somewhat faster than a method call:
C:\temp>\python24\lib\timeit.py -s "import t" "t.testMethod(t.instance,
42)"
1000 loops, best of 3: 1.58 msec per loop
C:\temp>\python24\lib\timeit.py -s "import t" "t.testMethod2(t.instance,
42)"
100 loops, best of 3: 1.61 msec per loop
C:\temp>\python24\lib\timeit.py -s "import t" "t.testNested(t.instance,
42)"
1000 loops, best of 3: 1.06 msec per loop
C:\temp>\python24\lib\timeit.py -s "import t" "t.testNested2(t.instance,
42)"
1000 loops, best of 3: 1.08 msec per loop
C:\temp>\python24\lib\timeit.py -s "import t" "t.testNested3(t.instance,
42)"
1000 loops, best of 3: 1.13 msec per loop
C:\temp>\python24\lib\timeit.py -s "import t" "t.testNested4(t.instance,
42)"
1000 loops, best of 3: 1.23 msec per loop
--------- t.py -------------
class C:
def m1(self):
return 42
def m2(self, x):
return x
instance = C()
def testMethod(instance,x):
n = 0
while n < 100000:
n += instance.m1()
def testMethod2(instance, x):
n = 0
while n < 100000:
n += instance.m2(x)
def testNested(instance, x):
def m1():
return 42
n = 0
while n < 100000:
n += m1()
def testNested2(instance, x):
def m2():
return x
n = 0
while n < 100000:
n += m2()
def testNested3(instance, x):
def m2(y):
return y
n = 0
while n < 100000:
n += m2(x)
def testNested4(instance, x):
def m2(y):
return x
n = 0
while n < 100000:
n += m2(x)
----------------------------
The differences between the nested function calls show how difficult it can
be guessing what will be faster: #3 show that all, else being equal,
accessing the closure is much slower than accessing a parameter, but #2
shows that not passing any parameters to the nested function more than
compensates for the single slow closure access.
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