From d3f8a5c7f637c06f5cb3d97fd76af7e6a34ee399 Mon Sep 17 00:00:00 2001
From: Gijs Burghoorn <me@gburghoorn.com>
Date: Tue, 24 Sep 2024 14:03:29 +0200
Subject: [PATCH] fix: Properly cast AnyValue string (#18888)

---
 crates/polars-core/src/datatypes/any_value.rs | 5 +++++
 crates/polars-python/src/dataframe/export.rs  | 6 +++---
 py-polars/tests/unit/test_convert.py          | 4 ++++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/crates/polars-core/src/datatypes/any_value.rs b/crates/polars-core/src/datatypes/any_value.rs
index fa8bf7caa3a1..83d9d4f8301d 100644
--- a/crates/polars-core/src/datatypes/any_value.rs
+++ b/crates/polars-core/src/datatypes/any_value.rs
@@ -563,6 +563,11 @@ impl<'a> AnyValue<'a> {
             (AnyValue::Float64(v), DataType::Boolean) => AnyValue::Boolean(*v != f64::default()),
 
             // to string
+            (AnyValue::String(v), DataType::String) => {
+                AnyValue::StringOwned(PlSmallStr::from_str(v))
+            },
+            (AnyValue::StringOwned(v), DataType::String) => AnyValue::StringOwned(v.clone()),
+
             (av, DataType::String) => {
                 if av.is_unsigned_integer() {
                     AnyValue::StringOwned(format_pl_smallstr!("{}", av.extract::<u64>()?))
diff --git a/crates/polars-python/src/dataframe/export.rs b/crates/polars-python/src/dataframe/export.rs
index cfd6feaa0138..c9fe0d4a48d0 100644
--- a/crates/polars-python/src/dataframe/export.rs
+++ b/crates/polars-python/src/dataframe/export.rs
@@ -49,15 +49,15 @@ impl PyDataFrame {
                 (0..df.height()).map(|idx| {
                     PyTuple::new_bound(
                         py,
-                        self.df.get_columns().iter().map(|s| match s.dtype() {
+                        self.df.get_columns().iter().map(|c| match c.dtype() {
                             DataType::Null => py.None(),
                             DataType::Object(_, _) => {
                                 let obj: Option<&ObjectValue> =
-                                    s.get_object(idx).map(|any| any.into());
+                                    c.get_object(idx).map(|any| any.into());
                                 obj.to_object(py)
                             },
                             // SAFETY: we are in bounds.
-                            _ => unsafe { Wrap(s.get_unchecked(idx)).into_py(py) },
+                            _ => unsafe { Wrap(c.get_unchecked(idx)).into_py(py) },
                         }),
                     )
                 }),
diff --git a/py-polars/tests/unit/test_convert.py b/py-polars/tests/unit/test_convert.py
index 0258ded0d18d..123c0a0cdebe 100644
--- a/py-polars/tests/unit/test_convert.py
+++ b/py-polars/tests/unit/test_convert.py
@@ -46,3 +46,7 @@ def test_from_dicts_all_cols_6716() -> None:
     ):
         pl.from_dicts(dicts, infer_schema_length=20)
     assert pl.from_dicts(dicts, infer_schema_length=None).dtypes == [pl.String]
+
+
+def test_dict_float_string_roundtrip_18882() -> None:
+    assert pl.from_dicts([{"A": "0.1"}]).to_dicts() == [{"A": "0.1"}]