is there such a built-in funciton, similar to filter

[Terry Reedy]

"Michael Hoffman" <cam.ac.uk at mh391.invalid> wrote in message 
news:dueg7q$o4p$1 at gemini.csx.cam.ac.uk...
> wcc wrote:
>
>> Beginner learning Python here.  I know filter(lambda x: x > 3, [1, 2,
>> 5, -3, 4, 8]) will give me a list [5, 4, 8].  What if I only need to
>> find the first item in the list that returns Ture when applying the
>> filter function.  In this case, I only want to get the 5, and its index

You have made two important changes to the function return value.
Filter returns a list of items.  You want an item and index.
What if there is no first item?

>> 2.  Is there a built-in function, or function from a module for that?
>> I think it is not hard to write a function for this.  But knowing
>> Python is "battery included", I thought I'd like to ask.

A 'battery' is something like the email, html, xml modules that assist 
major application areas.  Not every easily written 3-line function ;-)

> You can use a generator expression like this:
>
> >>> items = [1, 2, 5, -3, 4, 8]
> >>> ((index, item) for index, item in enumerate(items) if item > 
> >>> 3).next()
> (2, 5)

>>> items = [0,1,2,3]
>>> ((index, item) for index, item in enumerate(items) if item > 3).next()

Traceback (most recent call last):
  File "<pyshell#82>", line 1, in -toplevel-
    ((index, item) for index, item in enumerate(items) if item > 3).next()
StopIteration

I believe ifilter from the itertools module will act the same.

Terry Jan Reedy