> -----Original Message----- > From: Erik [mailto:pyt...@lucidity.plus.com] > Sent: Thursday, February 23, 2017 2:09 AM > To: pyt...@deborahswanson.net; python-list@python.org > Subject: Re: Namedtuples problem > > > Hi, > > On 23/02/17 09:38, Deborah Swanson wrote: > > group[[idx][records_idx[label]]] > > gets an IndexError: list index out of range > > [snip] > > > Can anyone see why I'm getting this Index error? and how to fix it? > > It looks to me like you are indexing into a single-element > list that you > are creating using the literal list syntax in the middle of > the expression.
Actually, group is essentially a 2-element list. Each group has a list of rows, and each row has a set of fields. group has to be indexed by row index and field index. (This is a namedtuple configuration.) The weirdness is that group[0][4] gets the right answer, but group[[idx][records_idx[label]]], where idx = 0 and records_idx[label]] = 4 gets the IndexError. > If we were to break the expression into parts to make it a > bit simpler > to refer to discuss: > > ridx = records_idx[label] > group[[idx][ridx]] > > You can now more easily see that 'group' is being indexed by the > expression "[idx][ridx]". What does that mean? > > [idx] is creating a single-element list using literal list > syntax. This > is then indexed using 'ridx' (using, perhaps confusingly, the > exact same > syntax to do a different thing). > > The result of *that* expression is then being used to index > 'group', but > it won't get that far because you'll get the exception if 'ridx' is > anything but zero. > > So the initial problem at least is the extra [] around 'idx' which is > creating a list on the fly for you. > > E. > -- https://mail.python.org/mailman/listinfo/python-list
