refactor[python]: Dispatch Series namespace methods to Expr using a d…

…ecorator (#4423)

py-polars/polars/internals/expr/categorical.py

@@ -11,6 +11,8 @@
 class ExprCatNameSpace:
     """Namespace for categorical related expressions."""
 
+    _accessor = "cat"
+
     def __init__(self, expr: pli.Expr):
         self._pyexpr = expr._pyexpr
 

py-polars/polars/internals/expr/datetime.py

@@ -14,6 +14,8 @@
 class ExprDateTimeNameSpace:
     """Namespace for datetime related expressions."""
 
+    _accessor = "dt"
+
     def __init__(self, expr: pli.Expr):
         self._pyexpr = expr._pyexpr
 

py-polars/polars/internals/expr/list.py

@@ -13,6 +13,8 @@
 class ExprListNameSpace:
     """Namespace for list related expressions."""
 
+    _accessor = "arr"
+
     def __init__(self, expr: pli.Expr):
         self._pyexpr = expr._pyexpr
 

py-polars/polars/internals/expr/meta.py

@@ -6,6 +6,8 @@
 class ExprMetaNameSpace:
     """Namespace for expressions on a meta level."""
 
+    _accessor = "meta"
+
     def __init__(self, expr: pli.Expr):
         self._pyexpr = expr._pyexpr
 

py-polars/polars/internals/expr/string.py

@@ -12,6 +12,8 @@
 class ExprStringNameSpace:
     """Namespace for string related expressions."""
 
+    _accessor = "str"
+
     def __init__(self, expr: pli.Expr):
         self._pyexpr = expr._pyexpr
 

py-polars/polars/internals/expr/struct.py

@@ -6,6 +6,8 @@
 class ExprStructNameSpace:
     """Namespace for struct related expressions."""
 
+    _accessor = "struct"
+
     def __init__(self, expr: pli.Expr):
         self._pyexpr = expr._pyexpr
 

py-polars/polars/internals/series/categorical.py

@@ -3,16 +3,21 @@
 from typing import TYPE_CHECKING
 
 import polars.internals as pli
+from polars.internals.series.utils import expr_dispatch
 
 if TYPE_CHECKING:
     from polars.internals.type_aliases import CategoricalOrdering
+    from polars.polars import PySeries
 
 
+@expr_dispatch
 class CatNameSpace:
     """Namespace for categorical related series."""
 
-    def __init__(self, s: pli.Series):
-        self._s = s
+    _accessor = "cat"
+
+    def __init__(self, series: pli.Series):
+        self._s: PySeries = series._s
 
     def set_ordering(self, ordering: CategoricalOrdering) -> pli.Series:
         """
@@ -55,4 +60,3 @@ def set_ordering(self, ordering: CategoricalOrdering) -> pli.Series:
         └──────┴──────┘
 
         """
-        return pli.select(pli.lit(self._s).cat.set_ordering(ordering)).to_series()