[Python-ideas] csv.DictReader could handle headers more intelligently.

Fri Jan 25 11:58:28 CET 2013

On Friday 25 Jan 2013, Ethan Furman wrote:
> On 01/24/2013 02:47 AM, Mark Hackett wrote:
> > On Thursday 24 Jan 2013, Steven D'Aprano wrote:
> >>> I'm not sure this behavior merits the all-caps "AS EXPECTED" label.
> >>> It's not terribly surprising once you sit down and think about it, but
> >>> it's certainly at least a little unexpected to me that data is being
> >>> thrown away with no notice. It's unusual for errors to pass silently
> >>> in python.
> >>
> >> Yes, we should not forget that a CSV file is not a dict. Just because
> >> DictReader is implemented with a dict as the storage, doesn't mean
> >> that it should behave exactly like a dict in all things. Multiple
> >> columns with the same name are legal in CSV, so there should be a reader
> >> for that situation.
> >
> > But just because it's reading a csv file, we shouldn't change how a
> > dictionary works if you add the same key again.
>> The proposal is not to change how a dict works, but what the proper
> response is for DictReader when a duplicate key is found.
>
Ethan, the proposal is predicated on the "silent abandonment" (which isn't 
actually the case any more than doing:
a=4
a=9
is abandoning silently the 4.) being unexpected.
Except, just like the assignment in the aside above, this is entirely what IS 
expected if you're putting a CSV line into a dictionary with duplicate key 
names.
If you don't want it to do what a dictionary does, then don't use DictReader, 
as Chris proposes.
My only niggle with that idea is that you'd be writing a lot of "SumptyReader" 
for each case and is redundant. But that may, in practice, be no problem at 
all.
If you didn't want it to do what a dict does, don't use a dict.