[Zope3-dev] Re: [z3-five] Re: Patch for testbrowser.py

[Tres Seaver]

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Paul Winkler wrote:
> On Fri, Apr 21, 2006 at 04:07:43PM +0200, Daniel Nouri wrote:
> 
>>The relevant code in Zope2's ZPublisher.HTTPResponse.__str__:
>>
>>        # ... we just built a headersl list using self.heders
>>        if self.cookies:
>>            headersl = headersl+self._cookie_list()
>>        headersl[len(headersl):] = [self.accumulated_headers, body]
>>        return '\n'.join(headersl)
>>
>>Maybe this can shed some light on whether we want to include that patch.
> 
> 
> As an aside:
> 
> What's with assigning to headersl[len(headersl):] instead of calling 
> headersl.extend(...)?
> 
> I've seen this idiom a couple of times and I always wonder
> why, it's much less readable IMO. 
> 
> I doubt it's supposed to be an optimization, since this code runs only
> once per request; anyway, the two idioms are about equivalent in speed
> AFAICT.
> 
> If it were in a performance-sensitive loop, a bit faster 
> and still quite readable would be:
> 
>     headersl += [self.accumulated_headers, body]
> 
> timeit confirms this, here on python 2.4.2:

I think this may be a fossil from a much earlier version of Python, in
which 'list.extend' had undesirable performance (the new one is
O(1)-amortized, I think).


Tres.
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Tres Seaver          +1 202-558-7113          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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