Extracting item from list of tuples?
__peter__ at web.de
Sun Sep 5 19:45:53 CEST 2010
Philip Semanchuk wrote:
> 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 for t in headers if t == 'location']
>> 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
This is actually more efficient because unlike Roy's (and your other
solution) it doesn't build a list, and it doesn't waste cycles in the loop
once the location is found. You can write it as a generator expression like
location = next((value for name, value in headers if name == "location"),
But just converting the headers to a dict is clearer and probably even
faster because it moves the loop from Python to C.
> If you prefer terse, IMHO this is less cryptic (but untested):
> location = [value for name, value in headers if name == 'location']
> 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.
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