Whilst considering a port of old code to python 3 I see that in several
places we are using type comparisons to control processing of user
instances (as opposed to instances of built in types eg float, int, str)
I find that the obvious alternatives are not as fast as the current
code; func0 below. On my machine isinstance seems slower than type for
some reason. My 2.6 timings are
C:\Tmp>\Python\lib\timeit.py -s"import t;v=t.X()" t.func0(v)
1000000 loops, best of 3: 0.348 usec per loop
C:\Tmp>\Python\lib\timeit.py -s"import t;v=t.X()" t.func1(v)
1000000 loops, best of 3: 0.747 usec per loop
C:\Tmp>\Python\lib\timeit.py -s"import t;v=t.X()" t.func2(v)
1000000 loops, best of 3: 0.378 usec per loop
C:\Tmp>\Python\lib\timeit.py -s"import t;v=t.X()" t.func3(v)
1000000 loops, best of 3: 0.33 usec per loop
C:\Tmp>\Python\lib\timeit.py -s"import t;v=t.X()" t.func0(1)
1000000 loops, best of 3: 0.477 usec per loop
C:\Tmp>\Python\lib\timeit.py -s"import t;v=t.X()" t.func1(1)
1000000 loops, best of 3: 1.14 usec per loop
C:\Tmp>\Python\lib\timeit.py -s"import t;v=t.X()" t.func2(1)
1000000 loops, best of 3: 1.16 usec per loop
C:\Tmp>\Python\lib\timeit.py -s"import t;v=t.X()" t.func3(1)
1000000 loops, best of 3: 1.14 usec per loop
so func 3 seems to be the fastest option for the case when the first
test matches, but is poor when it doesn't. Can anyone suggest a better
way to determine if an object is a user instance?
##############################
from types import InstanceType
class X:
__X__=True
class V(X):
pass
def func0(ob):
t=type(ob)
if t is InstanceType:
pass
elif t in (float, int):
pass
else:
pass
def func1(ob):
if isinstance(ob,X):
pass
elif type(ob) in (float, int):
pass
else:
pass
def func2(ob):
if getattr(ob,'__X__',False):
pass
elif type(ob) in (float, int):
pass
else:
pass
def func3(ob):
if hasattr(ob,'__X__'):
pass
elif type(ob) in (float, int):
pass
else:
pass
##############################
--
Robin Becker
--
http://mail.python.org/mailman/listinfo/python-list
