8000 Raise error in usecols when column doesn't exist but length matches by bpraggastis · Pull Request #16460 · pandas-dev/pandas · GitHub
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Raise error in usecols when column doesn't exist but length matches #16460

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Merged
merged 3 commits into from
Jun 4, 2017
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Raise error in usecols when column doesn't exist but length matches #16460

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812f928
gh-14671 Check if usecols with type string contains a subset of names…
brendapraggastis May 23, 2017
1968a70
tests added for gh-14671, expected behavior of simultaneous use of us…
brendapraggastis May 23, 2017
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TomAugspurger Jun 4, 2017
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tests added for gh-14671, expected behavior of simultaneous use of us… 
…ecols and names unclear so these tests are commented out
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@brendapraggastis @TomAugspurger
brendapraggastis authored and TomAugspurger committed Jun 4, 2017
commit 1968a70a4b821b0075d87c3b37e273ec876d84bf
32 changes: 29 additions & 3 deletions pandas/tests/io/parser/usecols.py
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Expand Up @@ -478,18 +478,44 @@ def test_uneven_length_cols(self):
tm.assert_frame_equal(df, expected)

def test_raise_on_usecols_names_mismatch(self):
# see gh-14671
## see gh-14671
data = 'a,b,c,d\n1,2,3,4\n5,6,7,8'
msg = 'Usecols do not match names' ## from parsers.py CParserWrapper()
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@gfyoung gfyoung May 24, 2017 •
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Condition the message on self.engine i.e.:

msg = <first-message> if self.engine == 'c' else <second-message>

That way you don't need that massive regex (and can remove the re import)

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do this one as well

msg2 = 'is not in list' ## from parser.py _handle_usecols()

usecols = ['a','b','c','d']
df = self.read_csv(StringIO(data), usecols=usecols)
expected = DataFrame({'a': [1,5], 'b': [2,6], 'c': [3,7], 'd': [4,8]})
tm.assert_frame_equal(df, expected)

msg = 'Usecols do not match names' ## from parsers.py CParserWrapper()
msg2 = 'is not in list' ## from parser.py _handle_usecols()
usecols = ['a','b','c','f']
with tm.assert_raises_regex(ValueError, re.compile("'" + msg + '||' + msg2 + "'")):
self.read_csv(StringIO(data), usecols=usecols)

usecols = ['a','b','f']
with tm.assert_raises_regex(ValueError, re.compile("'" + msg + '||' + msg2 + "'")):
self.read_csv(StringIO(data), usecols=usecols)

names = ['A', 'B', 'C', 'D']

df = self.read_csv(StringIO(data), header=0, names=names)
expected = DataFrame({'A': [1,5], 'B': [2,6], 'C': [3,7], 'D': [4,8]})
tm.assert_frame_equal(df, expected)

# usecols = ['A','C']
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commented out?

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Yes, those failures are related to #16469. Should put a TODO there I think.

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@bpraggastis I think add a TODO here with the issue above.

# df = self.read_csv(StringIO(data), header=0, names=names, usecols=usecols)
# expected = DataFrame({'A': [1,5], 'C': [3,7]})
# tm.assert_frame_equal(df, expected)
#
# usecols = [0,2]
# df = self.read_csv(StringIO(data), header=0, names=names, usecols=usecols)
# expected = DataFrame({'A': [1,5], 'C': [3,7]})
# tm.assert_frame_equal(df, expected)


usecols = ['A','B','C','f']
with tm.assert_raises_regex(ValueError, re.compile("'" + msg + '||' + msg2 + "'")):
self.read_csv(StringIO(data), header=0, names=names, usecols=usecols)
usecols = ['A','B','f']
with tm.assert_raises_regex(ValueError, re.compile("'" + msg + '||' + msg2 + "'")):
self.read_csv(StringIO(data), names=names, usecols=usecols)
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