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gh-138621: Increase test coverage for csv.DictReader and csv.Sniffer #138622

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gh-138621: Increase test coverage for csv.DictReader and csv.Sniffer #138622

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a796f9d
Increase test coverage for csv.DictReader and csv.Sniffer
JanEricNitschke Sep 7, 2025
22346fb
Revert whitespace change to comment
JanEricNitschke Sep 7, 2025
9d6d36f
Add a test that csv.Sniffer.has_header checks up to 20 rows
JanEricNitschke Sep 8, 2025
e44e9df
Replace name and age with letter and offset
JanEricNitschke Sep 8, 2025
ccf93cf
Address review comment
JanEricNitschke Sep 8, 2025
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18 changes: 17 additions & 1 deletion Lib/test/test_csv.py
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Original file line number Diff line number Diff line change
Expand Up @@ -918,6 +918,13 @@ def test_dict_reader_fieldnames_accepts_list(self):
reader = csv.DictReader(f, fieldnames)
self.assertEqual(reader.fieldnames, fieldnames)

def test_dict_reader_set_fieldnames(self):
fieldnames = ["a", "b", "c"]
f = StringIO()
reader = csv.DictReader(f)
reader.fieldnames = fieldnames
self.assertEqual(reader.fieldnames, fieldnames)

def test_dict_writer_fieldnames_rejects_iter(self):
fieldnames = ["a", "b", "c"]
f = StringIO()
Expand All @@ -933,6 +940,7 @@ def test_dict_writer_fieldnames_accepts_list(self):
def test_dict_reader_fieldnames_is_optional(self):
f = StringIO()
reader = csv.DictReader(f, fieldnames=None)
self.assertEqual(reader.fieldnames, None)

def test_read_dict_fields(self):
with TemporaryFile("w+", encoding="utf-8") as fileobj:
Expand All @@ -951,7 +959,7 @@ def test_read_dict_no_fieldnames(self):
self.assertEqual(reader.fieldnames, ["f1", "f2", "f3"])

# Two test cases to make sure existing ways of implicitly setting
# fieldnames continue to work. Both arise from discussion in issue3436.
# fieldnames continue to work. Both arise from discussion in issue3436.
def test_read_dict_fieldnames_from_file(self):
with TemporaryFile("w+", encoding="utf-8") as fileobj:
fileobj.write("f1,f2,f3\r\n1,2,abc\r\n")
Expand Down Expand Up @@ -1353,6 +1361,9 @@ class TestSniffer(unittest.TestCase):
ghi\0jkl
"""

sample15 = "\n\n\n"
sample16 = "abc\ndef\nghi"

def test_issue43625(self):
sniffer = csv.Sniffer()
self.assertTrue(sniffer.has_header(self.sample12))
Expand Down Expand Up @@ -1423,6 +1434,11 @@ def test_delimiters(self):
self.assertEqual(dialect.quotechar, "'")
dialect = sniffer.sniff(self.sample14)
self.assertEqual(dialect.delimiter, '\0')
self.assertRaisesRegex(csv.Error, "Could not determine delimiter",
sniffer.sniff, self.sample15)
self.assertRaisesRegex(csv.Error, "Could not determine delimiter",
sniffer.sniff, self.sample16)


def test_doublequote(self):
sniffer = csv.Sniffer()
Expand Down
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