empty clause of for loops

[Chris Angelico]

On Sat, Mar 19, 2016 at 7:49 AM, Sven R. Kunze <srkunze at mail.de> wrote:
> On 18.03.2016 20:10, Palpandi wrote:
>>
>> You can do like this.
>>
>> if not my_iterable:
>>      <do something>
>> for x in my_iterable:
>>      <do something>
>
>
> Thanks for you help here, however as already pointed out, my_iterable is not
> necessarily a list but more likely an exhaustible iterator/generator.

The sentinel option has already been mentioned:

x = sentinel = object()
for x in my_iterable:
    ...
if x is sentinel:
    was_empty

Python does offer another way to do this: instead of a sentinel
object, use an exception.

def process(iterable):
    """Process the iterable. If it was completely empty, raise
UnboundLocalError."""
    for x in iterable:
        ...
    x


Just for completeness :)

ChrisA