diff --git a/py-polars/polars/api.py b/py-polars/polars/api.py
index 97c45350d336..f1020b50bc09 100644
--- a/py-polars/polars/api.py
+++ b/py-polars/polars/api.py
@@ -43,7 +43,6 @@ def __get__(self, instance: NS | None, cls: type[NS]) -> NS | type[NS]:
             return self._ns
 
         ns_instance = self._ns(instance)  # type: ignore[call-arg]
-        setattr(instance, self._accessor, ns_instance)
         return ns_instance
 
 
diff --git a/py-polars/polars/dataframe/frame.py b/py-polars/polars/dataframe/frame.py
index 85337cf64d1d..dfe346d27710 100644
--- a/py-polars/polars/dataframe/frame.py
+++ b/py-polars/polars/dataframe/frame.py
@@ -347,6 +347,8 @@ class DataFrame:
     False
     """
 
+    __slots__ = ("_df",)
+    _df: PyDataFrame
     _accessors: ClassVar[set[str]] = {"plot"}
 
     def __init__(
diff --git a/py-polars/polars/datatypes/classes.py b/py-polars/polars/datatypes/classes.py
index d9e2fde8614c..9c22af7f0ad2 100644
--- a/py-polars/polars/datatypes/classes.py
+++ b/py-polars/polars/datatypes/classes.py
@@ -90,6 +90,8 @@ def is_nested(self) -> bool:  # noqa: D102
 class DataType(metaclass=DataTypeClass):
     """Base class for all Polars data types."""
 
+    __slots__ = ()
+
     def __reduce__(self) -> Any:
         return (_custom_reconstruct, (type(self), object, None), self.__dict__)
 
@@ -235,6 +237,7 @@ def _custom_reconstruct(
 class DataTypeGroup(frozenset):  # type: ignore[type-arg]
     """Group of data types."""
 
+    __slots__ = ("_match_base_type",)
     _match_base_type: bool
 
     def __new__(
@@ -267,70 +270,104 @@ def __contains__(self, item: Any) -> bool:
 class NumericType(DataType):
     """Base class for numeric data types."""
 
+    __slots__ = ()
+
 
 class IntegerType(NumericType):
     """Base class for integer data types."""
 
+    __slots__ = ()
+
 
 class SignedIntegerType(IntegerType):
     """Base class for signed integer data types."""
 
+    __slots__ = ()
+
 
 class UnsignedIntegerType(IntegerType):
     """Base class for unsigned integer data types."""
 
+    __slots__ = ()
+
 
 class FloatType(NumericType):
     """Base class for float data types."""
 
+    __slots__ = ()
+
 
 class TemporalType(DataType):
     """Base class for temporal data types."""
 
+    __slots__ = ()
+
 
 class NestedType(DataType):
     """Base class for nested data types."""
 
+    __slots__ = ()
+
 
 class Int8(SignedIntegerType):
     """8-bit signed integer type."""
 
+    __slots__ = ()
+
 
 class Int16(SignedIntegerType):
     """16-bit signed integer type."""
 
+    __slots__ = ()
+
 
 class Int32(SignedIntegerType):
     """32-bit signed integer type."""
 
+    __slots__ = ()
+
 
 class Int64(SignedIntegerType):
     """64-bit signed integer type."""
 
+    __slots__ = ()
+
 
 class UInt8(UnsignedIntegerType):
     """8-bit unsigned integer type."""
 
+    __slots__ = ()
+
 
 class UInt16(UnsignedIntegerType):
     """16-bit unsigned integer type."""
 
+    __slots__ = ()
+
 
 class UInt32(UnsignedIntegerType):
     """32-bit unsigned integer type."""
 
+    __slots__ = ()
+
 
 class UInt64(UnsignedIntegerType):
     """64-bit unsigned integer type."""
 
+    __slots__ = ()
+
 
 class Float32(FloatType):
     """32-bit floating point type."""
 
+    __slots__ = ()
+
 
 class Float64(FloatType):
     """64-bit floating point type."""
 
+    __slots__ = ()
+
 
 class Decimal(NumericType):
     """
@@ -342,6 +379,7 @@ class Decimal(NumericType):
         It may be changed at any point without it being considered a breaking change.
     """
 
+    __slots__ = ("precision", "scale")
     precision: int | None
     scale: int
 
@@ -383,10 +421,14 @@ def __hash__(self) -> int:
 class Boolean(DataType):
     """Boolean type."""
 
+    __slots__ = ()
+
 
 class String(DataType):
     """UTF-8 encoded string type."""
 
+    __slots__ = ()
+
 
 # Allow Utf8 as an alias for String
 Utf8 = String
@@ -395,14 +437,20 @@ class String(DataType):
 class Binary(DataType):
     """Binary type."""
 
+    __slots__ = ()
+
 
 class Date(TemporalType):
     """Calendar date type."""
 
+    __slots__ = ()
+
 
 class Time(TemporalType):
     """Time of day type."""
 
+    __slots__ = ()
+
 
 class Datetime(TemporalType):
     """Calendar date and time type."""
@@ -510,6 +558,7 @@ class Categorical(DataType):
             or string value (lexical).
     """
 
+    __slots__ = ("ordering",)
     ordering: CategoricalOrdering | None
 
     def __init__(
@@ -544,6 +593,7 @@ class Enum(DataType):
         It may be changed at any point without it being considered a breaking change.
     """
 
+    __slots__ = ("categories",)
     categories: Series
 
     def __init__(self, categories: Series | Iterable[str]):
@@ -606,14 +656,20 @@ def __repr__(self) -> str:
 class Object(DataType):
     """Type for wrapping arbitrary Python objects."""
 
+    __slots__ = ()
+
 
 class Null(DataType):
     """Type representing Null / None values."""
 
+    __slots__ = ()
+
 
 class Unknown(DataType):
     """Type representing Datatype values that could not be determined statically."""
 
+    __slots__ = ()
+
 
 class List(NestedType):
     """Variable length list type."""
@@ -738,6 +794,10 @@ def __repr__(self) -> str:
 class Field:
     """Definition of a single field within a `Struct` DataType."""
 
+    __slots__ = ("name", "dtype")
+    name: str
+    dtype: PolarsDataType
+
     def __init__(self, name: str, dtype: PolarsDataType):
         """
         Definition of a single field within a `Struct` DataType.
@@ -766,6 +826,7 @@ def __repr__(self) -> str:
 class Struct(NestedType):
     """Struct composite type."""
 
+    __slots__ = ("fields",)
     fields: list[Field]
 
     def __init__(self, fields: Sequence[Field] | SchemaDict):
diff --git a/py-polars/polars/expr/expr.py b/py-polars/polars/expr/expr.py
index d870bc8ca528..0e038427f8db 100644
--- a/py-polars/polars/expr/expr.py
+++ b/py-polars/polars/expr/expr.py
@@ -109,7 +109,8 @@
 class Expr:
     """Expressions that can be used in various contexts."""
 
-    _pyexpr: PyExpr = None
+    __slots__ = ("_pyexpr",)
+    _pyexpr: PyExpr
     _accessors: ClassVar[set[str]] = {
         "arr",
         "cat",
diff --git a/py-polars/polars/expr/whenthen.py b/py-polars/polars/expr/whenthen.py
index f357289fec46..ced5df6d68fe 100644
--- a/py-polars/polars/expr/whenthen.py
+++ b/py-polars/polars/expr/whenthen.py
@@ -24,6 +24,8 @@ class When:
     In this state, `then` must be called to continue to finish the expression.
     """
 
+    __slots__ = ("_when",)
+
     def __init__(self, when: Any):
         self._when = when
 
@@ -49,6 +51,8 @@ class Then(Expr):
     Represents the state of the expression after `pl.when(...).then(...)` is called.
     """
 
+    __slots__ = ("_then",)
+
     def __init__(self, then: Any):
         self._then = then
 
@@ -106,6 +110,8 @@ class ChainedWhen(Expr):
     In this state, `then` must be called to continue to finish the expression.
     """
 
+    __slots__ = ("_chained_when",)
+
     def __init__(self, chained_when: Any):
         self._chained_when = chained_when
 
@@ -131,6 +137,8 @@ class ChainedThen(Expr):
     Represents the state of the expression after an additional `then` is called.
     """
 
+    __slots__ = ("_chained_then",)
+
     def __init__(self, chained_then: Any):
         self._chained_then = chained_then
 
diff --git a/py-polars/polars/lazyframe/frame.py b/py-polars/polars/lazyframe/frame.py
index db79335f290f..7827ba8de667 100644
--- a/py-polars/polars/lazyframe/frame.py
+++ b/py-polars/polars/lazyframe/frame.py
@@ -286,6 +286,7 @@ class LazyFrame:
     └─────┴─────┴─────┘
     """
 
+    __slots__ = ("_ldf",)
     _ldf: PyLazyFrame
     _accessors: ClassVar[set[str]] = set()
 
diff --git a/py-polars/polars/selectors.py b/py-polars/polars/selectors.py
index 0793f5b9ee57..846dd4472bd6 100644
--- a/py-polars/polars/selectors.py
+++ b/py-polars/polars/selectors.py
@@ -242,6 +242,7 @@ def _combine_as_selector(
 class _selector_proxy_(Expr):
     """Base column selector expression/proxy."""
 
+    __slots__ = ("_attrs", "_repr_override")
     _attrs: dict[str, Any]
     _repr_override: str
 
diff --git a/py-polars/polars/series/series.py b/py-polars/polars/series/series.py
index 50c65d252255..4f6ba67f94ae 100644
--- a/py-polars/polars/series/series.py
+++ b/py-polars/polars/series/series.py
@@ -237,7 +237,8 @@ class Series:
     ]
     """
 
-    _s: PySeries = None
+    __slots__ = ("_s",)
+    _s: PySeries
     _accessors: ClassVar[set[str]] = {
         "arr",
         "cat",