MRAB wrote, on Thursday, February 23, 2017 4:06 PM > > On 2017-02-23 23:00, Deborah Swanson wrote: > > > > > >> -----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. > > > It's not weird. As Erik says below, and I'll repeat here, you have: > > group[[idx][records_idx[label]]] > > That consists of the expression: > > [idx][records_idx[label]] > > within: > > group[...] > > The [idx] creates a one-element list.
Yes, group[idx] gives you a row from group > You then try to subscript it with records_idx[label]. If > records_idx[label] is anything other than 0 (or -1), it'll raise > IndexError because there's only one element in that list. No, there are currently 17 elements in a record that records_idx[label] could be referring to in my running code, depending on which field 'label' refers to. Please see the breakdown of what a typical group looks like that I gave Steve. If you can't find it, let me know and I'll repeat it. > If you substitute idx == 0 and records_idx[label]] == 4 into: > > group[[idx][records_idx[label]]] > > you'll get: > > group[[0][4]] > > which is not the same thing as group[0][4]! No it isn't! And that's probably where the mysterious IndexError is coming from! Sickening how crosseyed I can get working with these things for too long at a stretch. And in fact, deleting that outer set of square brackets not only get's rid of the IndexError, but group[idx][records_idx[label]] now fers to the correct set of field values I was trying to access. Thank you, thank you! <snip> -- https://mail.python.org/mailman/listinfo/python-list
