On Wed, Dec 14, 2011 at 08:59:58PM -0400, Andre Roberge wrote:
> Personally, I find both the if/else and the try/except much easier to
> remember, and slightly easier to read than the one-liner.
>
> Furthermore, if one is interested in performance, it appears that the
> if/else approach is *always* faster than the one-liner. When exceptions
> are rarely raised, then the try/except approach is the fastest. Below are
> the results from a quick test to compare the efficiency of the three cases,
> followed by the code. This is using Python 2.7 on a fairly old computer.
>
> André
(Snipped André's code and results.)
Thanks for the benchmark!
For readability, my very favorite is to use defaultdict, in Python since
version 2.5:
from collections import defaultdict
d = defaultdict(int)
d[k] += 1
I added a defaultdict case to André's benchmark. It definitely beats
setdefault and is competitive with both try/except and if/else. This was
also run using Python 2.7 on my very slow notebook PC.
David H
===============================
100% new keys
setdefault: 0.821501894794
defaultdict: 0.96327996994
try/except: 3.30088125725
if/else: 0.400257295271
--------------------------------------------------
10% new keys
setdefault: 1.07847561631
defaultdict: 0.656087296011
try/except: 0.980378791159
if/else: 0.600138006367
--------------------------------------------------
1% new keys
setdefault: 1.08054654991
defaultdict: 0.604530464067
try/except: 0.711149322051
if/else: 0.605315759405
--------------------------------------------------
0.1% new keys
setdefault: 0.848571815692
defaultdict: 0.395037078735
try/except: 0.482041712005
if/else: 0.570016859685
===============================
from timeit import Timer
print "100% new keys\n"
print 'setdefault:\t',
t = Timer("""
d = {}
for i in range(1000):
d[i] = d.get(i, 0) + 1
""")
print t.timeit(number=1000)
print 'defaultdict:\t',
t = Timer("""
d = defaultdict(int)
for i in range(1000):
d[i] += 1
""", setup='from collections import defaultdict')
print t.timeit(number=1000)
print 'try/except:\t',
t = Timer("""
d = {}
for i in range(1000):
try:
d[i] += 1
except KeyError:
d[i] = 1
""")
print t.timeit(number=1000)
print 'if/else:\t',
t = Timer("""
d = {}
for i in range(1000):
if i in d:
d[i] += 1
else:
d[i] = 1
""")
print t.timeit(number=1000)
print "-"*50
print "10% new keys"
print 'setdefault:\t',
t = Timer("""
d = {}
for i in range(1000):
k = i % 100
d[k] = d.get(k, 0) + 1
""")
print t.timeit(number=1000)
print 'defaultdict:\t',
t = Timer("""
d = defaultdict(int)
for i in range(1000):
k = i % 100
d[k] += 1
""", setup='from collections import defaultdict')
print t.timeit(number=1000)
print 'try/except:\t',
t = Timer("""
d = {}
for i in range(1000):
k = i % 100
try:
d[k] += 1
except KeyError:
d[k] = 1
""")
print t.timeit(number=1000)
print 'if/else:\t',
t = Timer("""
d = {}
for i in range(1000):
k = i % 100
if i in d:
d[k] += 1
else:
d[k] = 1
""")
print t.timeit(number=1000)
print "-"*50
print "1% new keys\n"
print 'setdefault:\t',
t = Timer("""
d = {}
for i in range(1000):
k = i % 10
d[k] = d.get(k, 0) + 1
""")
print t.timeit(number=1000)
print 'defaultdict:\t',
t = Timer("""
d = defaultdict(int)
for i in range(1000):
k = i % 10
d[k] += 1
""", setup='from collections import defaultdict')
print t.timeit(number=1000)
print 'try/except:\t',
t = Timer("""
d = {}
for i in range(1000):
k = i % 10
try:
d[k] += 1
except KeyError:
d[k] = 1
""")
print t.timeit(number=1000)
print 'if/else:\t',
t = Timer("""
d = {}
for i in range(1000):
k = i % 10
if i in d:
d[k] += 1
else:
d[k] = 1
""")
print t.timeit(number=1000)
print "-"*50
print "0.1% new keys\n"
print 'setdefault:\t',
t = Timer("""
d = {}
for i in range(1000):
d[1] = d.get(1, 0) + 1
""")
print t.timeit(number=1000)
print 'defaultdict:\t',
t = Timer("""
d = defaultdict(int)
for i in range(1000):
d[1] += 1
""", setup='from collections import defaultdict')
print t.timeit(number=1000)
print 'try/except:\t',
t = Timer("""
d = {}
for i in range(1000):
try:
d[1] += 1
except KeyError:
d[1] = 1
""")
print t.timeit(number=1000)
print 'if/else:\t',
t = Timer("""
d = {}
for i in range(1000):
if 1 in d:
d[1] += 1
else:
d[1] = 1
""")
print t.timeit(number=1000)
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