My shot would be to test it like this on your platform like this:
#!/usr/bin/env python
import datetime, time
t1 = datetime.datetime.now()
for i in [str(x) for x in range(100)]:
if int(i) == i:
i + 1
t2 = datetime.datetime.now()
print t2 - t1
for i in [str(x) for x in range(100)]:
try:
int(i) +1
except:
pass
t3 = datetime.datetime.now()
print t3 - t2
for me (on python 2.4.1 on Linux on a AMD Sempron 2200+) it gives:
0:00:00.000637
0:00:00.000823
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