From 0d0a89825891aa88948d30ec1be29bdde9277451 Mon Sep 17 00:00:00 2001
From: Philippe Laflamme <philippe@hopper.com>
Date: Tue, 31 Jan 2023 09:26:28 -0500
Subject: [PATCH] feat: add DataType::Decimal128

---
 polars/polars-core/src/datatypes/dtype.rs |  8 ++++++++
 polars/polars-core/src/datatypes/mod.rs   | 13 +++++++++++--
 py-polars/src/conversion.rs               |  1 +
 py-polars/src/datatypes.rs                |  1 +
 py-polars/src/series.rs                   |  1 +
 5 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/polars/polars-core/src/datatypes/dtype.rs b/polars/polars-core/src/datatypes/dtype.rs
index f229301d752f..977a1c7697ff 100644
--- a/polars/polars-core/src/datatypes/dtype.rs
+++ b/polars/polars-core/src/datatypes/dtype.rs
@@ -15,6 +15,10 @@ pub enum DataType {
     Int64,
     Float32,
     Float64,
+    #[cfg(feature = "dtype-i128")]
+    /// Fixed point decimal type with precision and scale.
+    /// This is backed by 128 bits which allows for 38 significant digits.
+    Decimal128(Option<(usize, usize)>),
     /// String data
     Utf8,
     #[cfg(feature = "dtype-binary")]
@@ -208,6 +212,8 @@ impl DataType {
             Int64 => ArrowDataType::Int64,
             Float32 => ArrowDataType::Float32,
             Float64 => ArrowDataType::Float64,
+            #[cfg(feature = "dtype-i128")]
+            Decimal128(_) => todo!(),
             Utf8 => ArrowDataType::LargeUtf8,
             #[cfg(feature = "dtype-binary")]
             Binary => ArrowDataType::LargeBinary,
@@ -261,6 +267,8 @@ impl Display for DataType {
             DataType::Int64 => "i64",
             DataType::Float32 => "f32",
             DataType::Float64 => "f64",
+            #[cfg(feature = "dtype-i128")]
+            DataType::Decimal128(_) => "i128",
             DataType::Utf8 => "str",
             #[cfg(feature = "dtype-binary")]
             DataType::Binary => "binary",
diff --git a/polars/polars-core/src/datatypes/mod.rs b/polars/polars-core/src/datatypes/mod.rs
index 96dded32e0f4..e7ac00a0faf5 100644
--- a/polars/polars-core/src/datatypes/mod.rs
+++ b/polars/polars-core/src/datatypes/mod.rs
@@ -82,8 +82,6 @@ impl_polars_datatype!(Int8Type, Int8, i8);
 impl_polars_datatype!(Int16Type, Int16, i16);
 impl_polars_datatype!(Int32Type, Int32, i32);
 impl_polars_datatype!(Int64Type, Int64, i64);
-#[cfg(feature = "dtype-i128")]
-impl_polars_datatype!(Int128Type, Unknown, i128);
 impl_polars_datatype!(Float32Type, Float32, f32);
 impl_polars_datatype!(Float64Type, Float64, f64);
 impl_polars_datatype!(DateType, Date, i32);
@@ -120,6 +118,17 @@ impl PolarsDataType for ListType {
     }
 }
 
+#[cfg(feature = "dtype-i128")]
+pub struct Int128Type {}
+
+#[cfg(feature = "dtype-i128")]
+impl PolarsDataType for Int128Type {
+    fn get_dtype() -> DataType {
+        // we cannot know precision/scale statically
+        DataType::Decimal128(None)
+    }
+}
+
 #[cfg(feature = "object")]
 pub struct ObjectType<T>(T);
 #[cfg(feature = "object")]
diff --git a/py-polars/src/conversion.rs b/py-polars/src/conversion.rs
index 575d69fbd14e..56eebe940bb9 100644
--- a/py-polars/src/conversion.rs
+++ b/py-polars/src/conversion.rs
@@ -281,6 +281,7 @@ impl ToPyObject for Wrap<DataType> {
             DataType::UInt64 => pl.getattr("UInt64").unwrap().into(),
             DataType::Float32 => pl.getattr("Float32").unwrap().into(),
             DataType::Float64 => pl.getattr("Float64").unwrap().into(),
+            DataType::Decimal128(_) => todo!(),
             DataType::Boolean => pl.getattr("Boolean").unwrap().into(),
             DataType::Utf8 => pl.getattr("Utf8").unwrap().into(),
             DataType::Binary => pl.getattr("Binary").unwrap().into(),
diff --git a/py-polars/src/datatypes.rs b/py-polars/src/datatypes.rs
index 3e40787ce3e9..26a1c1b2f871 100644
--- a/py-polars/src/datatypes.rs
+++ b/py-polars/src/datatypes.rs
@@ -46,6 +46,7 @@ impl From<&DataType> for PyDataType {
             DataType::UInt64 => UInt64,
             DataType::Float32 => Float32,
             DataType::Float64 => Float64,
+            DataType::Decimal128(_) => todo!(),
             DataType::Boolean => Bool,
             DataType::Utf8 => Utf8,
             DataType::Binary => Binary,
diff --git a/py-polars/src/series.rs b/py-polars/src/series.rs
index 51758e0d0539..1c75a3eed603 100644
--- a/py-polars/src/series.rs
+++ b/py-polars/src/series.rs
@@ -666,6 +666,7 @@ impl PySeries {
                     DataType::Int64 => PyList::new(py, series.i64().unwrap()),
                     DataType::Float32 => PyList::new(py, series.f32().unwrap()),
                     DataType::Float64 => PyList::new(py, series.f64().unwrap()),
+                    DataType::Decimal128(_) => todo!(),
                     DataType::Categorical(_) => {
                         PyList::new(py, series.categorical().unwrap().iter_str())
                     }