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Date: Tue, 6 Oct 2015 00:51:51 +1100
Subject: Re: Finding Blank Columns in CSV
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Tue, Oct 6, 2015 at 12:48 AM, Chris Angelico <rosuav@gmail.com> wrote:
> fn = "tmp1.csv"
> fin = open(fn, 'rb')
> rdr = csv.DictReader(fin, delimiter=',')
> # all the same down to here
> blanks = set(rdr.fieldnames)
> for row in data:
>     blanks = {col for col in blanks if not row[col]}
> mt = [col for col in rdr.fieldnames if col not in blanks]
> print mt

Oops, premature send - hadn't proofread it yet.

fn = "tmp1.csv"
fin = open(fn, 'rb')
rdr = csv.DictReader(fin, delimiter=',')
# all the same down to here
blanks = set(rdr.fieldnames)
for row in rdr:
    blanks = {col for col in blanks if not row[col]}
mt = [col for col in rdr.fieldnames if col not in blanks]
print mt

Though I still haven't tested it, so there may be other bugs. Broadly
speaking, though, what it does is quite simple: start by assuming that
every column is nothing but blanks, and then any time you find a
non-blank cell, remove it from the set of blanks. At the end, all
field names not present in the set of blanks are non-blanks.

ChrisA