Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #20806

Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty

Followups directed to: comp.lang.python

Show key headers only | View raw

Rick Johnson wrote:

> On Feb 23, 6:30 pm, Alex Willmer <a...@moreati.org.uk> wrote:
>> [...]
>> as a standard looping-with-index construct. In Python for loops don't
>> create a scope, so the loop variables are available afterward. I've
>> sometimes used this to print or return a record count e.g.
>>
>> for i, x in enumerate(seq):
>> # do stuff
>> print 'Processed %i records' % i+1
> 
> You could employ the "else clause" of "for loops" to your advantage;

>>>> for x in []:
> ...     print x
> ... else:
> ...     print 'Empty Iterable'
> Empty Iterable
> 
>>>> for i,o in enumerate([]):
> ...     print i, o
> ... else:
> ...     print 'Empty Iterable'
> Empty Iterable

No:


>>> for i in []:
...     pass
... else:
...     print "else"
...
else
>>> for i in [42]:
...     pass
... else:
...     print "else"
...
else
>>> for i in [42]:
...     break
... else:
...     print "else"
...
>>>

The code in the else suite executes only when the for loop is left via 
break. A non-empty iterable is required but not sufficient.

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Alex Willmer <alex@moreati.org.uk> - 2012-02-23 16:30 -0800
  Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-24 01:08 +0000
    Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Ethan Furman <ethan@stoneleaf.us> - 2012-02-23 19:49 -0800
    Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-02-24 07:10 +0000
    Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Peter Otten <__peter__@web.de> - 2012-02-24 09:44 +0100
  Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Paul Rubin <no.email@nospam.invalid> - 2012-02-23 17:21 -0800
  Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Rick Johnson <rantingrickjohnson@gmail.com> - 2012-02-24 04:32 -0800
    Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Peter Otten <__peter__@web.de> - 2012-02-24 13:44 +0100
      Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Peter Otten <__peter__@web.de> - 2012-02-24 14:14 +0100
      Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-24 14:54 +0000
        Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Arnaud Delobelle <arnodel@gmail.com> - 2012-02-24 15:00 +0000
        Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Peter Otten <__peter__@web.de> - 2012-02-24 16:16 +0100
        Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Rick Johnson <rantingrickjohnson@gmail.com> - 2012-02-28 14:56 -0800
          Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Chris Angelico <rosuav@gmail.com> - 2012-02-29 10:24 +1100
            Re: A quirk/gotcha of for i, x in enumerate(seq) when seq is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-29 00:18 +0000

csiph-web