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BUG: Improve Error Message for Multi-Char Sep + Quotes in Python Engine #14582

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Nov 25, 2016
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BUG: Improve Error Message for Multi-Char Sep + Quotes in Python Engine #14582

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.19.2.txt
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Expand Up @@ -30,6 +30,7 @@ Bug Fixes
- Compat with ``dateutil==2.6.0``; segfault reported in the testing suite (:issue:`14621`)
- Allow ``nanoseconds`` in ``Timestamp.replace`` as a kwarg (:issue:`14621`)
- Bug in ``pd.read_csv`` where reading files fails, if the number of headers is equal to the number of lines in the file (:issue:`14515`)
- Bug in ``pd.read_csv`` for the Python engine in which an unhelpful error message was being raised when multi-char delimiters were not being respected with quotes (:issue:`14582`)



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5 changes: 5 additions & 0 deletions pandas/io/parsers.py
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Expand Up @@ -2515,6 +2515,11 @@ def _rows_to_cols(self, content):

msg = ('Expected %d fields in line %d, saw %d' %
(col_len, row_num + 1, zip_len))
if len(self.delimiter) > 1 and self.quoting != csv.QUOTE_NONE:
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Is the second part of the check needed (self.quoting != csv.QUOTE_NONE). Because AFAIU also when you do pass this, quotes are still be ignored by the regex expression to split the line, and you can still have this problem.

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@gfyoung gfyoung Nov 25, 2016 •
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@jorisvandenbossche : If quoting=csv.QUOTE_NONE, all quotation marks are treated as data, so that's the user's fault, not ours. That's why the check is necessary.

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Although it's a user error, you can still run into this problem so the message can still be useful I think. But I do see your point, so OK

# see gh-13374
reason = ('Error could possibly be due to quotes being '
'ignored when a multi-char delimiter is used.')
msg += '. ' + reason
raise ValueError(msg)

if self.usecols:
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17 changes: 17 additions & 0 deletions pandas/io/tests/parser/python_parser_only.py
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Expand Up @@ -7,6 +7,7 @@
arguments when parsing.
"""

import csv
import sys
import nose

Expand Down Expand Up @@ -204,3 +205,19 @@ def test_encoding_non_utf8_multichar_sep(self):
sep=sep, names=['a', 'b'],
encoding=encoding)
tm.assert_frame_equal(result, expected)

def test_multi_char_sep_quotes(self):
# see gh-13374

data = 'a,,b\n1,,a\n2,,"2,,b"'
msg = 'ignored when a multi-char delimiter is used'

with tm.assertRaisesRegexp(ValueError, msg):
self.read_csv(StringIO(data), sep=',,')

# We expect no match, so there should be an assertion
# error out of the inner context manager.
with tm.assertRaises(AssertionError):
with tm.assertRaisesRegexp(ValueError, msg):
self.read_csv(StringIO(data), sep=',,',
quoting=csv.QUOTE_NONE)