How to test if object is sequence, or iterable?

Collapse
This topic is closed.
X
X
Collapse
 
  • Page of 1
  • Time
  • Show
Clear All
new posts
Previous template Next
  • Tim N. van der Leeuw
    #1

    How to test if object is sequence, or iterable?

    Hi,

    I'd like to know if there's a way to check if an object is a sequence,
    or an iterable. Something like issequence() or isiterable().

    Does something like that exist? (Something which, in case of iterable,
    doesn't consume the first element of the iterable)

    Regards,

    --Tim

    Tags: python iterable
    • Bruno Desthuilliers
      #2
      Re: How to test if object is sequence, or iterable?

      Tim N. van der Leeuw a écrit :
      Hi,
      >
      I'd like to know if there's a way to check if an object is a sequence,
      or an iterable. Something like issequence() or isiterable().
      >
      Does something like that exist? (Something which, in case of iterable,
      doesn't consume the first element of the iterable)
      isiterable = lambda obj: isinstance(obj, basestring) \
      or getattr(obj, '__iter__', False)


      Should cover most cases.

        Comment

        • Tim N. van der Leeuw
          #3
          Re: How to test if object is sequence, or iterable?


          Bruno Desthuilliers wrote:
          Tim N. van der Leeuw a écrit :
          Hi,

          I'd like to know if there's a way to check if an object is a sequence,
          or an iterable. Something like issequence() or isiterable().

          Does something like that exist? (Something which, in case of iterable,
          doesn't consume the first element of the iterable)
          >
          isiterable = lambda obj: isinstance(obj, basestring) \
          or getattr(obj, '__iter__', False)
          >
          >
          Should cover most cases.
          Yes, that seems to cover all cases I can think of, indeed. Funny
          though, that string objects do not have an '__iter__' method, but are
          still iterable... But it will make most of my use-cases easier: Often I
          want to iterate over something, if it's an iterable, except when it's a
          string.


          Thanks,

          --Tim

            Comment

            • Terry Reedy
              #4
              Re: How to test if object is sequence, or iterable?


              "Tim N. van der Leeuw" <tim.leeuwvande r@nl.unisys.com wrote in message
              news:1153587482 .812348.320630@ h48g2000cwc.goo glegroups.com.. .
              Hi,
              >
              I'd like to know if there's a way to check if an object is a sequence,
              or an iterable. Something like issequence() or isiterable().
              How about
              try: it = iter(possible_i terable)
              except TypeError: bail()

              Terry Jan Reedy



                Comment

                • Marc 'BlackJack' Rintsch
                  #5
                  Re: How to test if object is sequence, or iterable?

                  In <44c26ec2$0$216 07$636a55ce@new s.free.fr>, Bruno Desthuilliers wrote:
                  Tim N. van der Leeuw a écrit :
                  >Hi,
                  >>
                  >I'd like to know if there's a way to check if an object is a sequence,
                  >or an iterable. Something like issequence() or isiterable().
                  >>
                  >Does something like that exist? (Something which, in case of iterable,
                  >doesn't consume the first element of the iterable)
                  >
                  isiterable = lambda obj: isinstance(obj, basestring) \
                  or getattr(obj, '__iter__', False)
                  >
                  >
                  Should cover most cases.
                  What about objects that just implement an apropriate `__getitem__()`
                  method?

                  Ciao,
                  Marc 'BlackJack' Rintsch

                    Comment

                    • Bruno Desthuilliers
                      #6
                      Re: How to test if object is sequence, or iterable?

                      Marc 'BlackJack' Rintsch a écrit :
                      In <44c26ec2$0$216 07$636a55ce@new s.free.fr>, Bruno Desthuilliers wrote:
                      >
                      >
                      >>Tim N. van der Leeuw a écrit :
                      >>
                      >>>Hi,
                      >>>
                      >>>I'd like to know if there's a way to check if an object is a sequence,
                      >>>or an iterable. Something like issequence() or isiterable().
                      >>>
                      >>>Does something like that exist? (Something which, in case of iterable,
                      >>>doesn't consume the first element of the iterable)
                      >>
                      >>isiterable = lambda obj: isinstance(obj, basestring) \
                      > or getattr(obj, '__iter__', False)
                      >>
                      >>
                      >>Should cover most cases.
                      >
                      >
                      What about objects that just implement an apropriate `__getitem__()`
                      method?
                      Hmmm... (quick test)

                      Good point.

                      FWIW, Terry's solution might be far better.

                        Comment

                        • Nick Vatamaniuc
                          #7
                          Re: How to test if object is sequence, or iterable?

                          Tim,

                          An object is iterable if it implements the iterator protocol. A good
                          enough check to see if it does is to check for the presense of the
                          __iter__() method. The way to do it is:
                          hasattr(object, '__iter__')

                          You are correct in the fact that you check if an object is iterable
                          rather than using isinstance to check if it is of a partucular type.
                          You are doing things 'the pythonic way' ;)

                          Nick Vatamaniuc


                          Tim N. van der Leeuw wrote:
                          Hi,
                          >
                          I'd like to know if there's a way to check if an object is a sequence,
                          or an iterable. Something like issequence() or isiterable().
                          >
                          Does something like that exist? (Something which, in case of iterable,
                          doesn't consume the first element of the iterable)
                          >
                          Regards,
                          >
                          --Tim

                            Comment

                            • Terry Reedy
                              #8
                              Re: How to test if object is sequence, or iterable?


                              "Nick Vatamaniuc" <vatamane@gmail .comwrote in message
                              news:1153604445 .246639.81270@h 48g2000cwc.goog legroups.com...
                              Tim,
                              >
                              An object is iterable if it implements the iterator protocol
                              There are presently two iterator protocols. The old one will be likely be
                              dropped in 3.0 (currently being discussed).
                              >. A good
                              enough check to see if it does is to check for the presense of the
                              __iter__() method. The way to do it is:
                              hasattr(object, '__iter__')
                              Sorry, this check for the newer and nicer protocol but not the older one.
                              >>hasattr('abc' , '__iter__')
                              False

                              This may change in 2.6. The defacto *version-independent* way to determine
                              iterability is to call iter(ob). If it returns an iterator, you can
                              iterate; if it raises TypeError, you cannot. Any it should be patched as
                              necessary by the developers to continue doing the right thing in future
                              versions.

                              Terry Jan Reedy



                                Comment

                                Previous template Next
                                Working...