Christopher Subich wrote:
> Peter Otten wrote:
>>
>> def add_freqs3(freq1, freq2):
>> total = dict(freq1)
>> for key, value in freq2.iteritems():
>> try:
>> total[key] += value
>> except KeyError:
>> total[key] = value
>> return total
>>
>
> Untested, but replacing the try/except pair with the following should be
> semantically equivalent and a bit faster:
>
> total[key] = total.get(key,0) + value
That depends on the data. For an 80/20 matches to misses ratio it ranges
between the two approaches I gave:
$ python -m timeit -r1 -n1 -s"from bm import fin as f" "f()"
1 loops, best of 1: 70.5 msec per loop
$ python -m timeit -r1 -n1 -s"from bm import fget as f" "f()"
1 loops, best of 1: 91.1 msec per loop
$ python -m timeit -r1 -n1 -s"from bm import fex as f" "f()"
1 loops, best of 1: 142 msec per loop
The break even for fget/fex is at about 92% hit rate:
$ python -m timeit -r1 -n1 -s"from bm import fget as f; d =
dict.fromkeys(range(92000), 0)" "f(d)"
1 loops, best of 1: 88 msec per loop
$ python -m timeit -r1 -n1 -s"from bm import fex as f; d =
dict.fromkeys(range(92000), 0)" "f(d)"
1 loops, best of 1: 87.4 msec per loop
Here's the bm.py module so you can verify my reasoning:
freqs = dict.fromkeys(range(8*10**4), 0)
keys = range(10**5)
def fin(d=freqs, keys=keys):
for key in keys:
if key in d:
d[key] += 42
else:
d[key] = 42
return d
def fget(d=freqs, keys=keys):
for key in keys:
d[key] = d.get(key, 0) + 42
return d
def fex(d=freqs, keys=keys):
for key in keys:
try:
d[key] += 42
except KeyError:
d[key] = 42
return d
if __name__ == "__main__":
assert fin(dict(freqs)) == fex(dict(freqs)) == fget(dict(freqs))
Peter
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