Extracting item from list of tuples?

Philip Semanchuk philip at semanchuk.com
Sun Sep 5 19:26:20 CEST 2010


On Sep 5, 2010, at 1:09 PM, Roy Smith wrote:

> I'm using httplib, and want to get the Location header from the
> response.  The getheaders() method gives you back a list of (name,
> value) tuples.  It would be a lot more convenient if it gave you  
> back a
> dict, but it is what it is.
>
> Anyway, I came up with:
>
>    location = [t[1] for t in headers if t[0] == 'location'][0]
>
> which works, but is getting on towards the cryptic end of things.  Is
> there a better idiom for this?

Are you concerned about efficiency? If it's not important, being less  
terse would make it less cryptic:
location = None
for name, value in headers:
    if name == "location":
       location = value
       break

If you prefer terse, IMHO this is less cryptic (but untested):

    location = [value for name, value in headers if name == 'location'] 
[0]


Be careful if you decide to turn the list of tuples into a dictionary.  
HTTP headers can repeat and straightforward code to turn the (name,  
value) pairs into a dict could end up overwriting data.

Cheers
P



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