From 38a8d0f7246bf6c5cba41e77d33fbdf25d8d5937 Mon Sep 17 00:00:00 2001
From: James Edwards <45176743+JamesCE2001@users.noreply.github.com>
Date: Sun, 21 Jul 2024 12:19:58 -0500
Subject: [PATCH] Fixed Categorical + Time reading/writing

---
 crates/polars-io/src/csv/read/read_impl.rs |  6 +++++
 crates/polars-io/src/csv/read/reader.rs    |  5 ++--
 py-polars/tests/unit/io/test_csv.py        | 27 +++++++++++++++++++++-
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/crates/polars-io/src/csv/read/read_impl.rs b/crates/polars-io/src/csv/read/read_impl.rs
index 50ba63dd668a..31e2cdc1ef4d 100644
--- a/crates/polars-io/src/csv/read/read_impl.rs
+++ b/crates/polars-io/src/csv/read/read_impl.rs
@@ -43,6 +43,12 @@ pub(crate) fn cast_columns(
                 .as_date(None, false)
                 .map(|ca| ca.into_series()),
             #[cfg(feature = "temporal")]
+            (DataType::String, DataType::Time) => s
+                .str()
+                .unwrap()
+                .as_time(None, false)
+                .map(|ca| ca.into_series()),
+            #[cfg(feature = "temporal")]
             (DataType::String, DataType::Datetime(tu, _)) => s
                 .str()
                 .unwrap()
diff --git a/crates/polars-io/src/csv/read/reader.rs b/crates/polars-io/src/csv/read/reader.rs
index 7de6d1ed58ff..88a3fe6786f8 100644
--- a/crates/polars-io/src/csv/read/reader.rs
+++ b/crates/polars-io/src/csv/read/reader.rs
@@ -170,9 +170,10 @@ impl<R: MmapBytesReader> CsvReader<R> {
 
                     match fld.data_type() {
                         Time => {
-                            self.options.fields_to_cast.push(fld);
+                            self.options.fields_to_cast.push(fld.clone());
                             // let inference decide the column type
-                            None
+                            fld.coerce(String);
+                            Some(Ok(fld))
                         },
                         #[cfg(feature = "dtype-categorical")]
                         Categorical(_, _) => {
diff --git a/py-polars/tests/unit/io/test_csv.py b/py-polars/tests/unit/io/test_csv.py
index 772a1ea74d7f..d352a7d8fd5a 100644
--- a/py-polars/tests/unit/io/test_csv.py
+++ b/py-polars/tests/unit/io/test_csv.py
@@ -2253,7 +2253,6 @@ def test_write_csv_raise_on_non_utf8_17328(
     with pytest.raises(InvalidOperationError, match="file encoding is not UTF-8"):
         df_no_lists.write_csv((tmp_path / "dangling.csv").open("w", encoding="gbk"))
 
-
 @pytest.mark.write_disk()
 def test_write_csv_appending_17543(tmp_path: Path) -> None:
     tmp_path.mkdir(exist_ok=True)
@@ -2264,3 +2263,29 @@ def test_write_csv_appending_17543(tmp_path: Path) -> None:
     with (tmp_path / "append.csv").open("r") as f:
         assert f.readline() == "# test\n"
         assert pl.read_csv(f).equals(df)
+
+@pytest.mark.parametrize(
+    ("dtype", "df"),
+    [
+        (pl.Decimal(scale=2), pl.DataFrame({"x": ["0.1"]}).cast(pl.Decimal(scale=2))),
+        (pl.Categorical, pl.DataFrame({"x": ["A"]})),
+        (
+            pl.Time,
+            pl.DataFrame({"x": ["12:15:00"]}).with_columns(
+                pl.col("x").str.strptime(pl.Time)
+            )
+        ),
+    ]
+)
+def test_read_csv_cast_unparsable_later(
+    tmp_path: Path,
+    dtype: pl.Decimal | pl.Categorical | pl.Time,
+    df: pl.DataFrame
+) -> None:
+    tmp_path.mkdir(exist_ok=True)
+    with (tmp_path / "append.csv").open("w") as f:
+        df.write_csv(f)
+    with (tmp_path / "append.csv").open("r") as f:
+        assert df.equals(
+            pl.read_csv(f, schema={"x": dtype})
+        )