Testing for an empty list
in [Python]
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From: Alexnb on 3 Jul 2008 16:58 Okay this is a simple question I just don't know how. If I have a list, say: funList = [] and after a while something possible should have been appended to it, but wasn't. How can I test if that list is empty. -- View this message in context: http://www.nabble.com/Testing-for-an-empty-list-tp18268092p18268092.html Sent from the Python - python-list mailing list archive at Nabble.com.
From: Matthew Fitzgibbons on 3 Jul 2008 17:05 Alexnb wrote: > Okay this is a simple question I just don't know how. If I have a list, say: > > funList = [] > > and after a while something possible should have been appended to it, but > wasn't. How can I test if that list is empty. if not funList: do_something() -Matt
From: Cameron Laird on 3 Jul 2008 22:02 In article <mailman.37.1215119171.20628.python-list(a)python.org>, Matthew Fitzgibbons <elessar(a)nienna.org> wrote: >Alexnb wrote: >> Okay this is a simple question I just don't know how. If I have a list, say: >> >> funList = [] >> >> and after a while something possible should have been appended to it, but >> wasn't. How can I test if that list is empty. > >if not funList: > do_something() . . . It's also perfectly legitimate--and arguably even more precise--to write if funList == []: do_something()
From: Roy Smith on 3 Jul 2008 22:26 In article <luc0k5-spf.ln1(a)lairds.us>, claird(a)lairds.us (Cameron Laird) wrote: > In article <mailman.37.1215119171.20628.python-list(a)python.org>, > Matthew Fitzgibbons <elessar(a)nienna.org> wrote: > >Alexnb wrote: > >> Okay this is a simple question I just don't know how. If I have a list, > >> say: > >> > >> funList = [] > >> > >> and after a while something possible should have been appended to it, but > >> wasn't. How can I test if that list is empty. > > > >if not funList: > > do_something() > . > . > . > It's also perfectly legitimate--and arguably even more > precise--to write > > if funList == []: > do_something() Any of these will be true for an empty list and false for a non-empty list: not funList len(funList) == 0 funList == [] Where they differ is how they behave for values of funList which are not lists. For example, if you did funList = (), then the first two would be true and the last one false. If you did funList = 0, the first and last would be true, and the middle one would raise an exception. The point is that if you're *sure* the item in question is going to be a list, then any of them are pretty much as good as any other. If it's a parameter that's being passed into a routine, so you can't be sure what type it is, then you should be thinking a little harder about how flexible you want to be.
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