How can I speed this function up?

nnorwitz at gmail.com nnorwitz at gmail.com
Sat Nov 18 11:20:46 CET 2006


Chris wrote:
> This is just some dummy code to mimic what's being done in the real
> code. The actual code is python which is used as a scripting language in
> a third party app. The data structure returned by the app is more or
> less like the "data" list in the code below. The test for "ELEMENT" is
> necessary ... it just evaluates to true every time in this test code. In
> the real app perhaps 90% of tests will also be true.

As others have said, without info about what's happening in C, there's
no way to know what's equivalent or fast enough.

> So my question is how can I speed up what's happening inside the
> function write_data()? Only allowed to use vanilla python (no psycho or
> other libraries outside of a vanilla python install).

Generally, don't create objects, don't perform repeated operations.  In
this case, batch up I/O.

> def write_data1(out, data):
>      for i in data:
>          if i[0] is 'ELEMENT':
>              out.write("%s %06d " % (i[0], i[1]))
>              for j in i[2]:
>                  out.write("%d " % (j))
>              out.write("\n")

def write_data1(out, data, map=map, str=str):
     SPACE_JOIN = ' '.join
     lines = [("ELEMENT %06d " % i1) + SPACE_JOIN(map(str, i2))
              for i0, i1, i2 in data if i0 == 'ELEMENT']
     out.write('\n'.join(lines))

While perhaps a bit obfuscated, it's a bit faster than the original.
Part of what makes this hard to read is the crappy variable names.  I
didn't know what to call them.  This version assumes that data will
always be a sequence of 3-element items.

The original version took about 11.5 seconds, the version above takes
just over 5 seconds.

YMMV,
n




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