[Python-Dev] Getting values stored inside sets

Sebastian Rittau srittau at jroger.in-berlin.de
Fri Apr 3 17:45:42 CEST 2009


On Fri, Apr 03, 2009 at 02:07:02PM +0200, Hrvoje Niksic wrote:

> But I can't seem to find a way to retrieve the element corresponding to  
> 'foo', at least not without iterating over the entire set.  Is this an  
> oversight or an intentional feature?  Or am I just missing an obvious  
> way to do this?

I am missing a simple way to retrieve the "first" element of any
iterable in python that matches a certain condition anyway. Something
like this:

  def first(iter, cb):
      for el in iter:
          if cb(el):
              return el
      raise IndexError()

Or (shorter, but potentially slower):

  def first(iter, cb):
      return [el for el in iter if cb(el)][0]

To be used like this:

  my_el = first(my_set, lambda el: el == "foobar")

This is something I need from time to time and this also seems to solve
your problem.

 - Sebastian

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