This is how the list of namedtuples is originally created from a csv:
infile = open("E:\\Coding projects\\Pycharm\\Moving\\Moving 2017 in -
test.csv")
rows = csv.reader(infile)fieldnames = next(rows)
Record = namedtuple("Record", fieldnames)
records = [Record._make(fieldnames)]
records.extend(Record._make(row) for row in rows)
Thanks to Peter Otten for this succinct code, and to Greg Ewing for
suggesting namedtuples for this type of problem to begin with.
Namedtuples worked beautifully for the first two thirds of this code,
but I've run into a snag attempting to proceed.
Here's my code up to the snag, and I'll explain afterwards what I'm
trying to do:
import operator
records[1:] = sorted(records[1:], key=operator.attrgetter("title",
"Date"))
groups = defaultdict()
for r in records[1:]:
# if the key doesn't exist, make a new group
if r.title not in groups.keys():
groups[r.title] = [r]
# if key (group) exists, append this record
else:
groups[r.title].append(r)
# make lookup table: indices for field names
records_idx = {}
for idx, label in enumerate(records[0]):
records_idx[label] = idx
LABELS = ['Location', 'ST', 'co', 'miles', 'first', 'Kind', 'Notes'] #
look at field values for each label on group for group in
groups.values():
values = []
for idx, row in enumerate(group):
for label in LABELS:
values.append(group[[idx][records_idx[label]]])
<-snag
I want to get lists of field values from the list of namedtuples, one
list of field values for each row in each group (groups are defined in
the section beginning with "groups = defaultdict()".
LABELS defines the field names for the columns of field values of
interest. So all the locations in this group would be in one list, all
the states in another list, etc. (Jussi, I'm looking at your suggestion
for the next part.)
(I'm quite sure this bit of code could be written with list and dict
comprehensions, but here I was just trying to get it to work, and
comprehensions still confuse me a little.)
Using the debugger's watch window, from
group[[idx][records_idx[label]]], I get:
idx = {int}: 0
records_idx[label] = {int}: 4
which is the correct indices for the first row of the current group (idx
= 0) and the first field label in LABELS, 'Location' (records_idx[label]
= 4).
And if I look at
group[0][4] = 'Longview'
this is also correct. Longview is the Location field value for the first
row of this group.
However,
group[[idx][records_idx[label]]]
gets an Index Error: list index out of range
I've run into this kind of problem with namedtuples before, trying to
access field values with variable names, like:
label = 'Location'
records.label
and I get something like "'records' has no attribute 'label'. This can
be fixed by using the subscript form and an index, like:
for idx, r in enumerate(records):
...
records[idx] = r
But here, I get the Index Error and I'm a bit baffled why. Both
subscripts evaluate to valid indices and give the correct value when
explicitly used.
Can anyone see why I'm getting this Index error? and how to fix it?
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