Appending to dictionary of lists

[Paul Rubin]

"Alex van der Spek" <zdoor at xs4all.nl> writes:
> refd=dict.fromkeys(csvr.fieldnames,[])  ...
> I do not understand why this appends v to every key k each time.

You have initialized every element of refd to the same list.  Try

    refd = dict((k,[]) for k in csvr.fieldnames)

instead.