Comments on: Collecting Python insights

By: Pablo

Pablo — Sat, 02 Aug 2008 08:09:05 +0000

defaultdict(int) is faster than defaultdict(lambda: 0)

By: Ivan

Ivan — Thu, 31 Jul 2008 05:49:31 +0000

Function reverse won’t work for UTF8 strings

By: Screwtape

Screwtape — Fri, 04 Jul 2008 11:45:50 +0000

The example for ‘Dynamic code evaluation’ is a good example of how to use exec, but a bad example of when exec is appropriate.The following code is a much nicer way of achieving the same thing, because it doesn’t involve exec and hence you never have to worry about people feeding it malicious strings:

def make_packet_extract(a, b):
____def foo(packet):
________return ord(packet[a]) + 256 * ord(packet[b])
____return foo

(apologies for the underscores,

didn’t seem to want to do its thing)

A better example for exec might be something where you have to change the actual structure of the method you’re building rather than just values within it - changing ‘and’ to ‘or’ or similar.

By: alain

alain — Fri, 04 Jul 2008 06:35:48 +0000

Python doesn’t have a reverse builtin but it has a reversed builtin:
for char in reversed(”hello world”):
print char

By: eliben

eliben — Fri, 04 Jul 2008 05:21:47 +0000

Mahadevan R:

The “insights” supposes RandomChunk already exists and can’t be modified.

By: eliben

eliben — Fri, 04 Jul 2008 05:21:17 +0000

JB:

As this benchmark demonstrates, you are quite wrong. xrange is faster (tried for both large and small LISTSIZE):

import timeit

setup = “”"
LISTSIZE = 10
“”"

s1 = “”"
k = 0
for i in range(LISTSIZE): k += i
“”"

s2 = “”"
k = 0
for i in xrange(LISTSIZE): k += i
“”"

N = 50000
print “range on integer”, timeit.Timer(stmt=s1, setup=setup).timeit(N)
print “xrange on integer”, timeit.Timer(stmt=s2, setup=setup).timeit(N)

By: Mahadevan R

Mahadevan R — Fri, 04 Jul 2008 04:40:17 +0000

In RandomChunker.chunk(), instead of “return ret”, do “yield ret”. Then, you can:

for chunk in rc.chunk():
print chunk

Cheers,
-Mahadevan.

By: JB

JB — Thu, 03 Jul 2008 18:05:34 +0000

xrange uses less memory, but it is slightly slower, as it needs to generate each value on demand.

Just sayin’.