read_csv(parse_dates=True) is broken for quoted dates

[stinodego]

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• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of Polars.

Issue description

I noticed this test during test suite cleanup. It passes when doing result.frame_equal(expected), but fails on assert_frame_equal.

The date column is not parsed correctly and is returned as a string.

Reproducible example

csv = textwrap.dedent(
    """a,b
"2022-01-01",1
"2022-01-02",2
"""
)
result = pl.read_csv(csv.encode(), parse_dates=True)
print(result)  # column 'a' is a string column, not date

# ┌────────────┬─────┐
# │ a          ┆ b   │
# │ ---        ┆ --- │
# │ str        ┆ i64 │
# ╞════════════╪═════╡
# │ 2022-01-01 ┆ 1   │
# │ 2022-01-02 ┆ 2   │
# └────────────┴─────┘

expected = pl.DataFrame({"a": [date(2022, 1, 1), date(2022, 1, 2)], "b": [1, 2]})
assert_frame_equal(result, expected)  # Fails

Expected behavior

I expect the column to be parsed as a date.

Installed versions

master branch

[MarcoGorelli]

Looks like this works as-expected in the latest release

In [11]: csv = textwrap.dedent(
    ...:     """a,b
    ...: "2022-01-01",1
    ...: "2022-01-02",2
    ...: """
    ...: )
    ...: result = pl.read_csv(csv.encode(), parse_dates=True)
    ...: print(result)  # column 'a' is a string column, not date
    ...:
shape: (2, 2)
┌────────────┬─────┐
│ a          ┆ b   │
│ ---        ┆ --- │
│ date       ┆ i64 │
╞════════════╪═════╡
│ 2022-01-01 ┆ 1   │
│ 2022-01-02 ┆ 2   │
└────────────┴─────┘

[stinodego]

Strange, it's still broken for me.

There is a test called test_quoted_date which is currently skipped - does it pass for you if you unskip it? If so, you can make a mini-PR removing the skip marker.

[MarcoGorelli]

Strange, it's still broken for me.

🤔 how odd, this works for me on both 0.16.3 and on master, for both Python 3.7 and 3.11

I'm running on Ubuntu (via WSL2). Any idea what else this could be down to?

[MarcoGorelli]

got it, it's just due to the indentation in the test