[issue3436] csv.DictReader inconsistency

[Andrii V. Mishkovskyi]

New submission from Andrii V. Mishkovskyi <mishok13 at gmail.com>:

I had to use csv module recently and ran into a "problem" with
DictReader. I had to get headers of CSV file and only after that iterate
throgh each row. But AFAIU there is no way to do it, other then
subclassing. So, basically, right now we have this:

Python 3.0b2+ (unknown, Jul 24 2008, 12:15:52)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import csv
>>> r = csv.DictReader(open('test.csv'))
>>> r.fieldnames
>>> next(r)
{'baz': '13', 'foo': '42', 'bar': '27'}
>>> r.fieldnames
['foo', 'bar', 'baz']

I think it would be much more useful, if DictReader got 'fieldnames' on
calling __init__ method, so this would look like this:
>>> r = csv.DictReader(open('test.csv'))
>>> r.fieldnames
['foo', 'bar', 'baz']

The easy way to do this is to subclass csv.DictReader.
The hard way to do this is to apply the patches I'm attaching. :)
These patches also remove redundant check for self.fieldnames being None
for each next()/__next__() call

----------
files: py3k.csv.py.diff
keywords: patch
messages: 70207
nosy: mishok13
severity: normal
status: open
title: csv.DictReader inconsistency
versions: Python 2.6, Python 3.0
Added file: http://bugs.python.org/file10965/py3k.csv.py.diff

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