From c8038653bc8f16e595d58ac530948b115fb197cd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <simon.hansen@me.com>
Date: Fri, 13 Dec 2024 12:14:33 +0100
Subject: [PATCH 01/11] playing around with types for parameters

---
 param/parameterized.py | 11 ++++++++---
 param/parameters.py    | 36 ++++++++++++++++++------------------
 2 files changed, 26 insertions(+), 21 deletions(-)

diff --git a/param/parameterized.py b/param/parameterized.py
index ac0df0343..f8fdf545e 100644
--- a/param/parameterized.py
+++ b/param/parameterized.py
@@ -29,6 +29,7 @@
 from itertools import chain
 from operator import itemgetter, attrgetter
 from types import FunctionType, MethodType
+from typing import TypeVar, Generic
 
 from contextlib import contextmanager
 from logging import DEBUG, INFO, WARNING, ERROR, CRITICAL
@@ -52,6 +53,8 @@
     gen_types,
 )
 
+T = TypeVar("T")
+
 # Ideally setting param_pager would be in __init__.py but param_pager is
 # needed on import to create the Parameterized class, so it'd need to precede
 # importing parameterized.py in __init__.py which would be a little weird.
@@ -1005,7 +1008,9 @@ def _sorter(p):
         cls.__signature__ = new_sig
 
 
-class Parameter(_ParameterBase):
+
+
+class Parameter(Generic[T], _ParameterBase):
     """
     An attribute descriptor for declaring parameters.
 
@@ -1431,7 +1436,7 @@ def _update_state(self):
         values, after the slot values have been set in the inheritance procedure.
         """
 
-    def __get__(self, obj, objtype): # pylint: disable-msg=W0613
+    def __get__(self, obj, objtype) -> T:
         """
         Return the value for this Parameter.
 
@@ -1455,7 +1460,7 @@ def __get__(self, obj, objtype): # pylint: disable-msg=W0613
         return result
 
     @instance_descriptor
-    def __set__(self, obj, val):
+    def __set__(self, obj, val: T) -> None:
         """
         Set the value for this Parameter.
 
diff --git a/param/parameters.py b/param/parameters.py
index 0259e2ae0..1f74dd421 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -36,7 +36,7 @@
 from .parameterized import (
     Parameterized, Parameter, ParameterizedFunction, ParamOverrides, String,
     Undefined, get_logger, instance_descriptor, _dt_types,
-    _int_types, _identity_hook
+    _int_types, _identity_hook, T
 )
 from ._utils import (
     ParamFutureWarning as _ParamFutureWarning,
@@ -451,7 +451,7 @@ def __exit__(self, exc, *args):
 #-----------------------------------------------------------------------------
 
 
-class Dynamic(Parameter):
+class Dynamic(Parameter[T]):
     """
     Parameter whose value can be generated dynamically by a callable
     object.
@@ -481,7 +481,7 @@ class Dynamic(Parameter):
 
     @typing.overload
     def __init__(
-        self, default=None, *,
+        self, default: T = None, *,
         doc=None, label=None, precedence=None, instantiate=False, constant=False,
         readonly=False, pickle_default_value=True, allow_None=False, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -515,7 +515,7 @@ def _initialize_generator(self,gen,obj=None):
         gen._saved_Dynamic_time = []
 
 
-    def __get__(self,obj,objtype):
+    def __get__(self, obj, objtype) -> T:
         """
         Call the superclass's __get__; if the result is not dynamic
         return that result, otherwise ask that result to produce a
@@ -530,7 +530,7 @@ def __get__(self,obj,objtype):
 
 
     @instance_descriptor
-    def __set__(self,obj,val):
+    def __set__(self, obj, val: T) -> None:
         """
         Call the superclass's set and keep this parameter's
         instantiate value up to date (dynamic parameters
@@ -624,7 +624,7 @@ def sig(self):
 _compute_set_hook = __compute_set_hook()
 
 
-class Number(Dynamic):
+class Number(Dynamic[T]):
     """
     A numeric Dynamic Parameter, with a default value and optional bounds.
 
@@ -679,7 +679,7 @@ class Number(Dynamic):
     @typing.overload
     def __init__(
         self,
-        default=0.0, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
+        default: T = 0.0, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -702,7 +702,7 @@ def __init__(self, default=Undefined, *, bounds=Undefined, softbounds=Undefined,
         self.step = step
         self._validate(self.default)
 
-    def __get__(self, obj, objtype):
+    def __get__(self, obj, objtype) -> T:
         """
         Same as the superclass's __get__, but if the value was
         dynamically generated, check the bounds.
@@ -838,7 +838,7 @@ def __setstate__(self,state):
 
 
 
-class Integer(Number):
+class Integer(Number[int]):
     """Numeric Parameter required to be an Integer"""
 
     _slot_defaults = dict(Number._slot_defaults, default=0)
@@ -887,7 +887,7 @@ def __init__(self, default=Undefined, *, bounds=Undefined, softbounds=Undefined,
         )
 
 
-class Date(Number):
+class Date(Number[T]):
     """Date parameter of datetime or date type."""
 
     _slot_defaults = dict(Number._slot_defaults, default=None)
@@ -895,7 +895,7 @@ class Date(Number):
     @typing.overload
     def __init__(
         self,
-        default=None, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
+        default: T = None, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
         doc=None, label=None, precedence=None, instantiate=False, constant=False,
         readonly=False, pickle_default_value=True, allow_None=False, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -1000,7 +1000,7 @@ def deserialize(cls, value):
 # Boolean
 #-----------------------------------------------------------------------------
 
-class Boolean(Parameter):
+class Boolean(Parameter[bool]):
     """Binary or tristate Boolean Parameter."""
 
     _slot_defaults = dict(Parameter._slot_defaults, default=False)
@@ -1099,7 +1099,7 @@ def _reset_event(self, obj, val):
         self._post_setter(obj, val)
 
     @instance_descriptor
-    def __set__(self, obj, val):
+    def __set__(self, obj, val: T) -> None:
         if self._mode in ['set-reset', 'set']:
             super().__set__(obj, val)
         if self._mode in ['set-reset', 'reset']:
@@ -1546,7 +1546,7 @@ def __init__(self, *, attribs=Undefined, **kw):
         super().__init__(default=Undefined, **kw)
         self.attribs = attribs
 
-    def __get__(self, obj, objtype):
+    def __get__(self, obj, objtype) -> T:
         """Return the values of all the attribs, as a list."""
         if obj is None:
             return [getattr(objtype, a) for a in self.attribs]
@@ -1576,7 +1576,7 @@ def _post_setter(self, obj, val):
 # Selector
 #-----------------------------------------------------------------------------
 
-class SelectorBase(Parameter):
+class SelectorBase(Parameter[T]):
     """
     Parameter whose value must be chosen from a list of possibilities.
 
@@ -2136,7 +2136,7 @@ def get_range(self):
         return _abbreviate_paths(self.path,super().get_range())
 
 
-class ClassSelector(SelectorBase):
+class ClassSelector(SelectorBase[T]):
     """
     Parameter allowing selection of either a subclass or an instance of a class or tuple of classes.
     By default, requires an instance, but if is_instance=False, accepts a class instead.
@@ -2151,7 +2151,7 @@ class ClassSelector(SelectorBase):
     @typing.overload
     def __init__(
         self,
-        *, class_, default=None, instantiate=True, is_instance=True,
+        *, class_, default: T = None, instantiate=True, is_instance=True,
         allow_None=False, doc=None, label=None, precedence=None,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -2743,7 +2743,7 @@ def _validate(self, val):
                 if self.check_exists:
                     raise OSError(e.args[0]) from None
 
-    def __get__(self, obj, objtype):
+    def __get__(self, obj, objtype) -> T:
         """Return an absolute, normalized path (see resolve_path)."""
         raw_path = super().__get__(obj,objtype)
         if raw_path is None:

From 8f46f78d77de459209ec41d5be9fd66d46f26e96 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <simon.hansen@me.com>
Date: Fri, 13 Dec 2024 13:12:22 +0100
Subject: [PATCH 02/11] Fix failing
 test_signature_parameters_constructors_overloaded_updated_match

---
 param/parameters.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/param/parameters.py b/param/parameters.py
index 1f74dd421..765dbb0e4 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -488,7 +488,7 @@ def __init__(
     ):
         ...
 
-    def __init__(self, default=Undefined, **params):
+    def __init__(self, default: T = Undefined, **params):
         """
         Call the superclass's __init__ and set instantiate=True if the
         default is dynamic.
@@ -687,7 +687,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, bounds=Undefined, softbounds=Undefined,
+    def __init__(self, default: T =Undefined, *, bounds=Undefined, softbounds=Undefined,
                  inclusive_bounds=Undefined, step=Undefined, set_hook=Undefined, **params):
         """
         Initialize this parameter object and store the bounds.
@@ -902,7 +902,7 @@ def __init__(
     ):
         ...
 
-    def __init__(self, default=Undefined, **kwargs):
+    def __init__(self, default: T = Undefined, **kwargs):
         super().__init__(default=default, **kwargs)
 
     def _validate_value(self, val, allow_None):
@@ -2159,7 +2159,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, *, class_, default=Undefined, instantiate=Undefined, is_instance=Undefined, **params):
+    def __init__(self, *, class_, default: T = Undefined, instantiate=Undefined, is_instance=Undefined, **params):
         self.class_ = class_
         self.is_instance = is_instance
         super().__init__(default=default,instantiate=instantiate,**params)

From e74ae5921b5854d470e78af8b6f0848e9c8921fe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <simon.hansen@me.com>
Date: Fri, 13 Dec 2024 13:31:28 +0100
Subject: [PATCH 03/11] Update list

---
 param/parameters.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/param/parameters.py b/param/parameters.py
index 765dbb0e4..a83f3e771 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -2444,7 +2444,7 @@ def _validate(self, val):
 # List
 #-----------------------------------------------------------------------------
 
-class List(Parameter):
+class List(Parameter[T]):
     """
     Parameter whose value is a list of objects, usually of a specified type.
 
@@ -2467,7 +2467,7 @@ class List(Parameter):
     @typing.overload
     def __init__(
         self,
-        default=[], *, class_=None, item_type=None, instantiate=True, bounds=(0, None),
+        default: T = [], *, class_=None, item_type=None, instantiate=True, bounds=(0, None),
         allow_None=False, doc=None, label=None, precedence=None,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -2475,7 +2475,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, class_=Undefined, item_type=Undefined,
+    def __init__(self, default: T = Undefined, *, class_=Undefined, item_type=Undefined,
                  instantiate=Undefined, bounds=Undefined, **params):
         if class_ is not Undefined:
             # PARAM3_DEPRECATION

From 5915224f93660f8bcddde1778dce9e0bb3150628 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <simon.hansen@me.com>
Date: Mon, 16 Dec 2024 14:48:58 +0100
Subject: [PATCH 04/11] Add more typevar T to classes

---
 param/parameterized.py |   6 +--
 param/parameters.py    | 114 ++++++++++++++++++++---------------------
 2 files changed, 60 insertions(+), 60 deletions(-)

diff --git a/param/parameterized.py b/param/parameterized.py
index f8fdf545e..8844d238d 100644
--- a/param/parameterized.py
+++ b/param/parameterized.py
@@ -1608,7 +1608,7 @@ def __setstate__(self,state):
 
 
 # Define one particular type of Parameter that is used in this file
-class String(Parameter):
+class String(Parameter[T]):
     r"""
     A String Parameter, with a default value and optional regular expression (regex) matching.
 
@@ -1629,7 +1629,7 @@ def __init__(self, default="0.0.0.0", allow_None=False, **kwargs):
     @typing.overload
     def __init__(
         self,
-        default="", *, regex=None,
+        default: T = "", *, regex=None,
         doc=None, label=None, precedence=None, instantiate=False, constant=False,
         readonly=False, pickle_default_value=True, allow_None=False, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -1637,7 +1637,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, regex=Undefined, **kwargs):
+    def __init__(self, default: T = Undefined, *, regex=Undefined, **kwargs):
         super().__init__(default=default, **kwargs)
         self.regex = regex
         self._validate(self.default)
diff --git a/param/parameters.py b/param/parameters.py
index a83f3e771..62ac8891b 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -864,7 +864,7 @@ def _validate_step(self, val, step):
             )
 
 
-class Magnitude(Number):
+class Magnitude(Number[T]):
     """Numeric Parameter required to be in the range [0.0-1.0]."""
 
     _slot_defaults = dict(Number._slot_defaults, default=1.0, bounds=(0.0,1.0))
@@ -872,14 +872,14 @@ class Magnitude(Number):
     @typing.overload
     def __init__(
         self,
-        default=1.0, *, bounds=(0.0, 1.0), softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
+        default: T = 1.0, *, bounds=(0.0, 1.0), softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
     ):
         ...
 
-    def __init__(self, default=Undefined, *, bounds=Undefined, softbounds=Undefined,
+    def __init__(self, default: T = Undefined, *, bounds=Undefined, softbounds=Undefined,
                  inclusive_bounds=Undefined, step=Undefined, set_hook=Undefined, **params):
         super().__init__(
             default=default, bounds=bounds, softbounds=softbounds,
@@ -946,7 +946,7 @@ def deserialize(cls, value):
         return dt.datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%f")
 
 
-class CalendarDate(Number):
+class CalendarDate(Number[T]):
     """Parameter specifically allowing dates (not datetimes)."""
 
     _slot_defaults = dict(Number._slot_defaults, default=None)
@@ -954,14 +954,14 @@ class CalendarDate(Number):
     @typing.overload
     def __init__(
         self,
-        default=None, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
+        default: T = None, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
         doc=None, label=None, precedence=None, instantiate=False, constant=False,
         readonly=False, pickle_default_value=True, allow_None=False, per_instance=True,
         allow_refs=False, nested_refs=False
     ):
         ...
 
-    def __init__(self, default=Undefined, **kwargs):
+    def __init__(self, default: T = Undefined, **kwargs):
         super().__init__(default=default, **kwargs)
 
     def _validate_value(self, val, allow_None):
@@ -1000,7 +1000,7 @@ def deserialize(cls, value):
 # Boolean
 #-----------------------------------------------------------------------------
 
-class Boolean(Parameter[bool]):
+class Boolean(Parameter[T]):
     """Binary or tristate Boolean Parameter."""
 
     _slot_defaults = dict(Parameter._slot_defaults, default=False)
@@ -1008,7 +1008,7 @@ class Boolean(Parameter[bool]):
     @typing.overload
     def __init__(
         self,
-        default=False, *,
+        default: T = False, *,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -1016,7 +1016,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, **params):
+    def __init__(self, default: T = Undefined, **params):
         super().__init__(default=default, **params)
         self._validate(self.default)
 
@@ -1037,7 +1037,7 @@ def _validate(self, val):
         self._validate_value(val, self.allow_None)
 
 
-class Event(Boolean):
+class Event(Boolean[T]):
     """
     An Event Parameter is one whose value is intimately linked to the
     triggering of events for watchers to consume. Event has a Boolean
@@ -1061,7 +1061,7 @@ class Event(Boolean):
     @typing.overload
     def __init__(
         self,
-        default=False, *,
+        default: T = False, *,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -1069,7 +1069,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self,default=False,**params):
+    def __init__(self, default: T = False, **params):
         self._autotrigger_value = True
         self._autotrigger_reset_value = False
         self._mode = 'set-reset'
@@ -1124,7 +1124,7 @@ def sig(self):
 _compute_length_of_default = __compute_length_of_default()
 
 
-class Tuple(Parameter):
+class Tuple(Parameter[T]):
     """A tuple Parameter (e.g. ('a',7.6,[3,5])) with a fixed tuple length."""
 
     __slots__ = ['length']
@@ -1134,7 +1134,7 @@ class Tuple(Parameter):
     @typing.overload
     def __init__(
         self,
-        default=(0,0), *, length=None,
+        default: T = (0,0), *, length=None,
         doc=None, label=None, precedence=None, instantiate=False, constant=False,
         readonly=False, pickle_default_value=True, allow_None=False, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -1142,7 +1142,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, length=Undefined, **params):
+    def __init__(self, default: T = Undefined, *, length=Undefined, **params):
         """
         Initialize a tuple parameter with a fixed length (number of
         elements).  The length is determined by the initial default
@@ -1198,7 +1198,7 @@ def deserialize(cls, value):
         return tuple(value) # As JSON has no tuple representation
 
 
-class NumericTuple(Tuple):
+class NumericTuple(Tuple[T]):
     """A numeric tuple Parameter (e.g. (4.5,7.6,3)) with a fixed tuple length."""
 
     def _validate_value(self, val, allow_None):
@@ -1214,7 +1214,7 @@ def _validate_value(self, val, allow_None):
             )
 
 
-class XYCoordinates(NumericTuple):
+class XYCoordinates(NumericTuple[T]):
     """A NumericTuple for an X,Y coordinate."""
 
     _slot_defaults = dict(NumericTuple._slot_defaults, default=(0.0, 0.0))
@@ -1222,18 +1222,18 @@ class XYCoordinates(NumericTuple):
     @typing.overload
     def __init__(
         self,
-        default=(0.0, 0.0), *, length=None,
+        default: T = (0.0, 0.0), *, length=None,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
     ):
         ...
 
-    def __init__(self, default=Undefined, **params):
+    def __init__(self, default: T = Undefined, **params):
         super().__init__(default=default, length=2, **params)
 
 
-class Range(NumericTuple):
+class Range(NumericTuple[T]):
     """A numeric range with optional bounds and softbounds."""
 
     __slots__ = ['bounds', 'inclusive_bounds', 'softbounds', 'step']
@@ -1246,7 +1246,7 @@ class Range(NumericTuple):
     @typing.overload
     def __init__(
         self,
-        default=None, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, length=None,
+        default: T = None, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, length=None,
         doc=None, label=None, precedence=None, instantiate=False, constant=False,
         readonly=False, pickle_default_value=True, allow_None=False, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -1254,7 +1254,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, bounds=Undefined, softbounds=Undefined,
+    def __init__(self, default: T = Undefined, *, bounds=Undefined, softbounds=Undefined,
                  inclusive_bounds=Undefined, step=Undefined, **params):
         self.bounds = bounds
         self.inclusive_bounds = inclusive_bounds
@@ -1464,7 +1464,7 @@ def deserialize(cls, value):
 # Callable
 #-----------------------------------------------------------------------------
 
-class Callable(Parameter):
+class Callable(Parameter[T]):
     """
     Parameter holding a value that is a callable object, such as a function.
 
@@ -1477,7 +1477,7 @@ class Callable(Parameter):
     @typing.overload
     def __init__(
         self,
-        default=None, *,
+        default: T = None, *,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -1485,7 +1485,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, **params):
+    def __init__(self, default: T = Undefined, **params):
         super().__init__(default=default, **params)
         self._validate(self.default)
 
@@ -1811,7 +1811,7 @@ def _modified_slots_defaults(cls):
         return defaults
 
 
-class Selector(SelectorBase, _SignatureSelector):
+class Selector(SelectorBase[T], _SignatureSelector):
     """
     Parameter whose value must be one object from a list of possible objects.
 
@@ -1845,7 +1845,7 @@ class Selector(SelectorBase, _SignatureSelector):
     @typing.overload
     def __init__(
         self,
-        *, objects=[], default=None, instantiate=False, compute_default_fn=None,
+        *, objects=[], default: T = None, instantiate=False, compute_default_fn=None,
         check_on_set=None, allow_None=None, empty_default=False,
         doc=None, label=None, precedence=None, constant=False, readonly=False,
         pickle_default_value=True, per_instance=True, allow_refs=False, nested_refs=False
@@ -1855,7 +1855,7 @@ def __init__(
     # Selector is usually used to allow selection from a list of
     # existing objects, therefore instantiate is False by default.
     @_deprecate_positional_args
-    def __init__(self, *, objects=Undefined, default=Undefined, instantiate=Undefined,
+    def __init__(self, *, objects=Undefined, default: T = Undefined, instantiate=Undefined,
                  compute_default_fn=Undefined, check_on_set=Undefined,
                  allow_None=Undefined, empty_default=False, **params):
 
@@ -1981,7 +1981,7 @@ def __init__(self, default=Undefined, *, objects=Undefined, **kwargs):
                          empty_default=True, **kwargs)
 
 
-class FileSelector(Selector):
+class FileSelector(Selector[T]):
     """Given a path glob, allows one file to be selected from those matching."""
 
     __slots__ = ['path']
@@ -1993,7 +1993,7 @@ class FileSelector(Selector):
     @typing.overload
     def __init__(
         self,
-        default=None, *, path="", objects=[], instantiate=False, compute_default_fn=None,
+        default: T =None, *, path="", objects=[], instantiate=False, compute_default_fn=None,
         check_on_set=None, allow_None=None, empty_default=False,
         doc=None, label=None, precedence=None, constant=False, readonly=False,
         pickle_default_value=True, per_instance=True, allow_refs=False, nested_refs=False
@@ -2001,7 +2001,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, path=Undefined, **kwargs):
+    def __init__(self, default: T = Undefined, *, path=Undefined, **kwargs):
         self.default = default
         self.path = path
         self.update(path=path)
@@ -2032,7 +2032,7 @@ def get_range(self):
         return _abbreviate_paths(self.path,super().get_range())
 
 
-class ListSelector(Selector):
+class ListSelector(Selector[T]):
     """
     Variant of Selector where the value can be multiple objects from
     a list of possible objects.
@@ -2041,7 +2041,7 @@ class ListSelector(Selector):
     @typing.overload
     def __init__(
         self,
-        default=None, *, objects=[], instantiate=False, compute_default_fn=None,
+        default: T =None, *, objects=[], instantiate=False, compute_default_fn=None,
         check_on_set=None, allow_None=None, empty_default=False,
         doc=None, label=None, precedence=None, constant=False, readonly=False,
         pickle_default_value=True, per_instance=True, allow_refs=False, nested_refs=False
@@ -2049,7 +2049,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, objects=Undefined, **kwargs):
+    def __init__(self, default: T = Undefined, *, objects=Undefined, **kwargs):
         super().__init__(
             objects=objects, default=default, empty_default=True, **kwargs)
 
@@ -2090,7 +2090,7 @@ def _update_state(self):
                 self._ensure_value_is_in_objects(o)
 
 
-class MultiFileSelector(ListSelector):
+class MultiFileSelector(ListSelector[T]):
     """Given a path glob, allows multiple files to be selected from the list of matches."""
 
     __slots__ = ['path']
@@ -2102,7 +2102,7 @@ class MultiFileSelector(ListSelector):
     @typing.overload
     def __init__(
         self,
-        default=None, *, path="", objects=[], compute_default_fn=None,
+        default: T = None, *, path="", objects=[], compute_default_fn=None,
         check_on_set=None, allow_None=None, empty_default=False,
         doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True,
@@ -2111,7 +2111,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, path=Undefined, **kwargs):
+    def __init__(self, default: T = Undefined, *, path=Undefined, **kwargs):
         self.default = default
         self.path = path
         self.update(path=path)
@@ -2211,31 +2211,31 @@ class Dict(ClassSelector):
     @typing.overload
     def __init__(
         self,
-        default=None, *, is_instance=True,
+        default: T = None, *, is_instance=True,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=True,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
     ):
         ...
 
-    def __init__(self, default=Undefined, **params):
+    def __init__(self, default: T = Undefined, **params):
         super().__init__(default=default, class_=dict, **params)
 
 
-class Array(ClassSelector):
+class Array(ClassSelector[T]):
     """Parameter whose value is a numpy array."""
 
     @typing.overload
     def __init__(
         self,
-        default=None, *, is_instance=True,
+        default: T = None, *, is_instance=True,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=True,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
     ):
         ...
 
-    def __init__(self, default=Undefined, **params):
+    def __init__(self, default: T = Undefined, **params):
         from numpy import ndarray
         super().__init__(default=default, class_=ndarray, **params)
 
@@ -2259,7 +2259,7 @@ def deserialize(cls, value):
             return numpy.asarray(value)
 
 
-class DataFrame(ClassSelector):
+class DataFrame(ClassSelector[T]):
     """
     Parameter whose value is a pandas DataFrame.
 
@@ -2287,7 +2287,7 @@ class DataFrame(ClassSelector):
     @typing.overload
     def __init__(
         self,
-        default=None, *, rows=None, columns=None, ordered=None, is_instance=True,
+        default: T =None, *, rows=None, columns=None, ordered=None, is_instance=True,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=True,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -2295,7 +2295,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, rows=Undefined, columns=Undefined, ordered=Undefined, **params):
+    def __init__(self, default: T = Undefined, *, rows=Undefined, columns=Undefined, ordered=Undefined, **params):
         from pandas import DataFrame as pdDFrame
         self.rows = rows
         self.columns = columns
@@ -2385,7 +2385,7 @@ def deserialize(cls, value):
             return pandas.DataFrame(value)
 
 
-class Series(ClassSelector):
+class Series(ClassSelector[T]):
     """
     Parameter whose value is a pandas Series.
 
@@ -2403,7 +2403,7 @@ class Series(ClassSelector):
     @typing.overload
     def __init__(
         self,
-        default=None, *, rows=None, allow_None=False, is_instance=True,
+        default: T = None, *, rows=None, allow_None=False, is_instance=True,
         doc=None, label=None, precedence=None, instantiate=True,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -2411,7 +2411,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, rows=Undefined, allow_None=Undefined, **params):
+    def __init__(self, default: T = Undefined, *, rows=Undefined, allow_None=Undefined, **params):
         from pandas import Series as pdSeries
         self.rows = rows
         super().__init__(default=default, class_=pdSeries, allow_None=allow_None,
@@ -2670,7 +2670,7 @@ def __call__(self,path="",**params):
 
 
 
-class Path(Parameter):
+class Path(Parameter[T]):
     """
     Parameter that can be set to a string specifying the path of a file or folder.
 
@@ -2708,7 +2708,7 @@ class Path(Parameter):
     @typing.overload
     def __init__(
         self,
-        default=None, *, search_paths=None, check_exists=True,
+        default: T = None, *, search_paths=None, check_exists=True,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -2716,7 +2716,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, search_paths=Undefined, check_exists=Undefined, **params):
+    def __init__(self, default: T = Undefined, *, search_paths=Undefined, check_exists=Undefined, **params):
         if search_paths is Undefined:
             search_paths = []
 
@@ -2816,7 +2816,7 @@ def _resolve(self, path):
 # Color
 #-----------------------------------------------------------------------------
 
-class Color(Parameter):
+class Color(Parameter[T]):
     """
     Color parameter defined as a hex RGB string with an optional #
     prefix or (optionally) as a CSS3 color name.
@@ -2866,7 +2866,7 @@ class Color(Parameter):
     @typing.overload
     def __init__(
         self,
-        default=None, *, allow_named=True,
+        default: T = None, *, allow_named=True,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -2874,7 +2874,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, allow_named=Undefined, **kwargs):
+    def __init__(self, default: T = Undefined, *, allow_named=Undefined, **kwargs):
         super().__init__(default=default, **kwargs)
         self.allow_named = allow_named
         self._validate(self.default)
@@ -2912,7 +2912,7 @@ def _validate_allow_named(self, val, allow_named):
 # Bytes
 #-----------------------------------------------------------------------------
 
-class Bytes(Parameter):
+class Bytes(Parameter[T]):
     """
     A Bytes Parameter, with a default value and optional regular
     expression (regex) matching.
@@ -2931,7 +2931,7 @@ class Bytes(Parameter):
     @typing.overload
     def __init__(
         self,
-        default=b"", *, regex=None, allow_None=False,
+        default: T = b"", *, regex=None, allow_None=False,
         doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -2939,7 +2939,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, default=Undefined, *, regex=Undefined, allow_None=Undefined, **kwargs):
+    def __init__(self, default: T = Undefined, *, regex=Undefined, allow_None=Undefined, **kwargs):
         super().__init__(default=default, **kwargs)
         self.regex = regex
         self._validate(self.default)

From 694523812203d1d9304eda3599d85728a6b94751 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <simon.hansen@me.com>
Date: Mon, 16 Dec 2024 14:57:58 +0100
Subject: [PATCH 05/11] Use T for Integer

---
 param/parameters.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/param/parameters.py b/param/parameters.py
index 62ac8891b..c896c6b0a 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -838,7 +838,7 @@ def __setstate__(self,state):
 
 
 
-class Integer(Number[int]):
+class Integer(Number[T]):
     """Numeric Parameter required to be an Integer"""
 
     _slot_defaults = dict(Number._slot_defaults, default=0)

From 30f45acb3c5bbe803e4224a2add6142f1afcc7b5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <simon.hansen@me.com>
Date: Mon, 16 Dec 2024 16:19:13 +0100
Subject: [PATCH 06/11] Update __init__ for Integer

---
 param/parameters.py | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/param/parameters.py b/param/parameters.py
index c896c6b0a..7b92f021b 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -15,6 +15,7 @@
 parameter types (e.g. Number), and also imports the definition of
 Parameters and Parameterized classes.
 """
+from __future__ import annotations
 
 import collections
 import copy
@@ -843,6 +844,19 @@ class Integer(Number[T]):
 
     _slot_defaults = dict(Number._slot_defaults, default=0)
 
+    @typing.overload
+    def __init__(
+        self,
+        default: T = 0, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
+        allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
+        constant=False, readonly=False, pickle_default_value=True, per_instance=True,
+        allow_refs=False, nested_refs=False
+    ):
+        ...
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
     def _validate_value(self, val, allow_None):
         if callable(val):
             return

From 1d2ed5fb496a50b05df1eed7d866c7a91c1ec927 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <simon.hansen@me.com>
Date: Mon, 16 Dec 2024 16:19:45 +0100
Subject: [PATCH 07/11] Add type_information to ClassSelector

---
 param/parameters.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/param/parameters.py b/param/parameters.py
index 7b92f021b..131d760a3 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -2165,7 +2165,7 @@ class ClassSelector(SelectorBase[T]):
     @typing.overload
     def __init__(
         self,
-        *, class_, default: T = None, instantiate=True, is_instance=True,
+        *, class_: tuple[type[T], ...] | type[T], default: T = None, instantiate=True, is_instance=True,
         allow_None=False, doc=None, label=None, precedence=None,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
@@ -2173,7 +2173,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, *, class_, default: T = Undefined, instantiate=Undefined, is_instance=Undefined, **params):
+    def __init__(self, *, class_: tuple[type[T]] | type[T], default: T = Undefined, instantiate=Undefined, is_instance=Undefined, **params):
         self.class_ = class_
         self.is_instance = is_instance
         super().__init__(default=default,instantiate=instantiate,**params)

From a2bd29b2144600bb32441064356a88252f488753 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <simon.hansen@me.com>
Date: Mon, 16 Dec 2024 16:40:19 +0100
Subject: [PATCH 08/11] fix tests

---
 param/parameters.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/param/parameters.py b/param/parameters.py
index 131d760a3..508159ac4 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -854,8 +854,8 @@ def __init__(
     ):
         ...
 
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
+    def __init__(self, default: T = Undefined, *args, **kwargs):
+        super().__init__(default=default, *args, **kwargs)
 
     def _validate_value(self, val, allow_None):
         if callable(val):
@@ -2173,7 +2173,7 @@ def __init__(
         ...
 
     @_deprecate_positional_args
-    def __init__(self, *, class_: tuple[type[T]] | type[T], default: T = Undefined, instantiate=Undefined, is_instance=Undefined, **params):
+    def __init__(self, *, class_: tuple[type[T], ...] | type[T], default: T = Undefined, instantiate=Undefined, is_instance=Undefined, **params):
         self.class_ = class_
         self.is_instance = is_instance
         super().__init__(default=default,instantiate=instantiate,**params)

From 8d72d1fd61767c23805fc74354c4a04dcbd97cec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <hoxbro@protonmail.com>
Date: Tue, 17 Jun 2025 11:34:52 +0200
Subject: [PATCH 09/11] Dirty hack for setting non value

---
 param/parameters.py | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/param/parameters.py b/param/parameters.py
index 508159ac4..2a4b8b8a6 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -877,6 +877,11 @@ def _validate_step(self, val, step):
                 f"None or an integer value, not {type(step)}."
             )
 
+    def __set__(self, obj, val: T | int) -> None:
+        if typing.TYPE_CHECKING:
+            val = typing.cast("T", val)
+        super().__set__(obj, val)
+
 
 class Magnitude(Number[T]):
     """Numeric Parameter required to be in the range [0.0-1.0]."""
@@ -1526,7 +1531,7 @@ class Action(Callable):
 # Composite
 #-----------------------------------------------------------------------------
 
-class Composite(Parameter):
+class Composite(Parameter[T]):
     """
     A Parameter that is a composite of a set of other attributes of the class.
 

From 6bd00461a93ac6ed9d8f3b5fc833ec38d665c02b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <hoxbro@protonmail.com>
Date: Tue, 1 Jul 2025 17:26:21 +0200
Subject: [PATCH 10/11] Fix lint

---
 param/parameterized.py | 2 +-
 param/parameters.py    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/param/parameterized.py b/param/parameterized.py
index e8b4dfbcc..246788761 100644
--- a/param/parameterized.py
+++ b/param/parameterized.py
@@ -27,7 +27,7 @@
 from itertools import chain
 from operator import itemgetter, attrgetter
 from types import FunctionType, MethodType
-from typing import Any, Union, Literal  # When python 3.9 support is dropped replace Union with |
+from typing import Any, Union, Literal, Generic, TypeVar  # When python 3.9 support is dropped replace Union with |
 
 from contextlib import contextmanager
 CRITICAL = 50
diff --git a/param/parameters.py b/param/parameters.py
index 38a40b7a7..66b1da965 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -849,7 +849,7 @@ def __setstate__(self,state):
 
 
 class Integer(Number[T]):
-    """Numeric Parameter required to be an Integer"""
+    """Numeric Parameter required to be an Integer."""
 
     _slot_defaults = dict(Number._slot_defaults, default=0)
 

From 205a9ad0da29c841380d25d41a095797f00d391e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8xbro=20Hansen?= <hoxbro@protonmail.com>
Date: Wed, 2 Jul 2025 10:16:08 +0200
Subject: [PATCH 11/11] Playing around

---
 param/parameterized.py |  4 +--
 param/parameters.py    | 61 +++++++++++++++++++++++++++++++++++++-----
 2 files changed, 56 insertions(+), 9 deletions(-)

diff --git a/param/parameterized.py b/param/parameterized.py
index 246788761..465747d99 100644
--- a/param/parameterized.py
+++ b/param/parameterized.py
@@ -231,7 +231,7 @@ def _identity_hook(obj, val):
     return val
 
 
-class _Undefined:
+class _TUndefined:
     """
     Dummy value to signal completely undefined values rather than
     simple None values.
@@ -247,7 +247,7 @@ def __repr__(self):
         return '<Undefined>'
 
 
-Undefined = _Undefined()
+Undefined = _TUndefined()
 
 
 @contextmanager
diff --git a/param/parameters.py b/param/parameters.py
index 66b1da965..099232984 100644
--- a/param/parameters.py
+++ b/param/parameters.py
@@ -37,7 +37,7 @@
 from .parameterized import (
     Parameterized, Parameter, ParameterizedFunction, ParamOverrides, String,
     Undefined, get_logger, instance_descriptor, _dt_types,
-    _int_types, _identity_hook, T
+    _int_types, _identity_hook, T, _TUndefined
 )
 from ._utils import (
     ParamFutureWarning as _ParamFutureWarning,
@@ -847,8 +847,12 @@ def __setstate__(self,state):
         super().__setstate__(state)
 
 
+import typing as t
+# int = t.TypeVar("_TInteger", bound="int")
+# int = t.TypeVar("_TInteger", bound="int")
+_TNone = t.Literal[None]
 
-class Integer(Number[T]):
+class Integer(Number[int]):
     """Numeric Parameter required to be an Integer."""
 
     _slot_defaults = dict(Number._slot_defaults, default=0)
@@ -856,16 +860,51 @@ class Integer(Number[T]):
     @typing.overload
     def __init__(
         self,
-        default: T = 0, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
+        default: int = 0,
+        *args,
+        allow_None: typing.Literal[False] = ...,
+        **kwargs
+    ) -> None: ...
+
+    @typing.overload
+    def __init__(
+        self,
+        default: int | _TNone = 0,
+        *args,
+        allow_None: typing.Literal[True] = ...,
+        **kwargs
+    ) -> None: ...
+
+    @typing.overload
+    def __init__(
+        self,
+        default: int | _TNone = None,
+        *args,
+        allow_None: typing.Literal[True] = True,
+        **kwargs
+    ) -> None: ...
+
+    @typing.overload
+    def __init__(
+        self,
+        default: int = 0, *, bounds=None, softbounds=None, inclusive_bounds=(True,True), step=None, set_hook=None,
         allow_None=False, doc=None, label=None, precedence=None, instantiate=False,
         constant=False, readonly=False, pickle_default_value=True, per_instance=True,
         allow_refs=False, nested_refs=False
     ):
         ...
 
-    def __init__(self, default: T = Undefined, *args, **kwargs):
+    def __init__(self, default: int | _TNone | _TUndefined = Undefined, *args, allow_None = False, **kwargs):
+        if typing.TYPE_CHECKING:
+            # self.__allow_None = allow_None
+            if isinstance(default, _TUndefined):
+                default = 0
+
         super().__init__(default=default, *args, **kwargs)
 
+        # if typing.TYPE_CHECKING:
+        #     self.__allow_None = allow_None
+        #
     def _validate_value(self, val, allow_None):
         if callable(val):
             return
@@ -886,9 +925,17 @@ def _validate_step(self, val, step):
                 f"None or an integer value, not {type(step)}."
             )
 
-    def __set__(self, obj, val: T | int) -> None:
-        if typing.TYPE_CHECKING:
-            val = typing.cast("T", val)
+    def __set__(self, obj, val: int | None) -> None:
+        # if typing.TYPE_CHECKING:
+        #     if val is None and not self.__allow_None:
+        #             raise TypeError("None is not allowed")
+        #         # else:
+        #         #     value = typing.cast("_TNone", value)
+        #     if val is not None:
+        #         if type(val) is not int:
+        #             raise TypeError("Only int allowed")
+        #         # else:
+        #         #     value = typing.cast("int", val)
         super().__set__(obj, val)