Generic parameter

docs/changes/newsfragments/7730.improved

@@ -0,0 +1,4 @@
+The QCoDeS Parameter classes ``ParameterBase``, ``Parameter``, ``ParameterWithSetpoints``, ``DelegateParameter``, ``ArrayParameter`` and ``MultiParameter`` now
+takes two Optional Generic arguments to allow the data type and the type of the instrument the parameter is bound to to be fixed statically. This enables
+the type of the output of ``parameter.get()``, input of ``parameter.set()`` and value of ``parameter.instrument`` to be known statically such that type
+checkers and IDE's can make use of this information.

src/qcodes/parameters/array_parameter.py

@@ -12,15 +12,14 @@
     has_loop = True
 except ImportError:
     has_loop = False
+from typing import Generic
 
-from .parameter_base import ParameterBase
+from .parameter_base import InstrumentTypeVar_co, ParameterBase, ParameterDataTypeVar
 from .sequence_helpers import is_sequence_of
 
 if TYPE_CHECKING:
     from collections.abc import Mapping, Sequence
 
-    from qcodes.instrument import InstrumentBase
-
 
 try:
     from qcodes_loop.data.data_array import DataArray
@@ -41,7 +40,10 @@
     )
 
 
-class ArrayParameter(ParameterBase):
+class ArrayParameter(
+    ParameterBase[ParameterDataTypeVar, InstrumentTypeVar_co],
+    Generic[ParameterDataTypeVar, InstrumentTypeVar_co],
+):
     """
     A gettable parameter that returns an array of values.
     Not necessarily part of an instrument.
@@ -131,7 +133,9 @@ def __init__(
         self,
         name: str,
         shape: Sequence[int],
-        instrument: InstrumentBase | None = None,
+        # mypy seems to be confused here. The bound and default for InstrumentTypeVar_co
+        # contains None but mypy will not allow it as a default as of v 1.19.0
+        instrument: InstrumentTypeVar_co = None,  # type: ignore[assignment]
         label: str | None = None,
         unit: str | None = None,
         setpoints: Sequence[Any] | None = None,

src/qcodes/parameters/cache.py

@@ -1,14 +1,22 @@
 from __future__ import annotations
 
 from datetime import datetime, timedelta
-from typing import TYPE_CHECKING, Protocol
+from typing import TYPE_CHECKING, Any, Generic, Literal, Protocol, overload
+
+from typing_extensions import TypeVar
+
+# due to circular imports we cannot import the TypeVar from parameter_base
+ParameterDataTypeVar = TypeVar("ParameterDataTypeVar", default=Any)
 
 if TYPE_CHECKING:
-    from .parameter_base import ParamDataType, ParameterBase, ParamRawDataType
+    from .parameter_base import (
+        ParameterBase,
+        ParamRawDataType,
+    )
 
 
 # The protocol is private to qcodes but used elsewhere in the codebase
-class _CacheProtocol(Protocol):  # noqa: PYI046
+class _CacheProtocol(Protocol, Generic[ParameterDataTypeVar]):  # noqa: PYI046
     """
     This protocol defines the interface that a Parameter Cache implementation
     must implement. This is currently used for 2 implementations, one in
@@ -29,24 +37,36 @@ def valid(self) -> bool: ...
 
     def invalidate(self) -> None: ...
 
-    def set(self, value: ParamDataType) -> None: ...
+    def set(self, value: ParameterDataTypeVar) -> None: ...
 
     def _set_from_raw_value(self, raw_value: ParamRawDataType) -> None: ...
 
-    def get(self, get_if_invalid: bool = True) -> ParamDataType: ...
+    @overload
+    def get(self, get_if_invalid: Literal[True]) -> ParameterDataTypeVar: ...
+
+    @overload
+    def get(self) -> ParameterDataTypeVar: ...
+
+    @overload
+    def get(self, get_if_invalid: Literal[False]) -> ParameterDataTypeVar | None: ...
+
+    @overload
+    def get(self, get_if_invalid: bool) -> ParameterDataTypeVar | None: ...
+
+    def get(self, get_if_invalid: bool = True) -> ParameterDataTypeVar | None: ...
 
     def _update_with(
         self,
         *,
-        value: ParamDataType,
+        value: ParameterDataTypeVar,
         raw_value: ParamRawDataType,
         timestamp: datetime | None = None,
     ) -> None: ...
 
-    def __call__(self) -> ParamDataType: ...
+    def __call__(self) -> ParameterDataTypeVar: ...
 
 
-class _Cache:
+class _Cache(Generic[ParameterDataTypeVar]):
     """
     Cache object for parameter to hold its value and raw value
 
@@ -66,9 +86,11 @@ class _Cache:
 
     """
 
-    def __init__(self, parameter: ParameterBase, max_val_age: float | None = None):
+    def __init__(
+        self, parameter: ParameterBase, max_val_age: float | None = None
+    ) -> None:
         self._parameter = parameter
-        self._value: ParamDataType = None
+        self._value: ParameterDataTypeVar | None = None
         self._raw_value: ParamRawDataType = None
         self._timestamp: datetime | None = None
         self._max_val_age = max_val_age
@@ -115,7 +137,7 @@ def invalidate(self) -> None:
         """
         self._marked_valid = False
 
-    def set(self, value: ParamDataType) -> None:
+    def set(self, value: ParameterDataTypeVar) -> None:
         """
         Set the cached value of the parameter without invoking the
         ``set_cmd`` of the parameter (if it has one). For example, in case of
@@ -146,7 +168,7 @@ def _set_from_raw_value(self, raw_value: ParamRawDataType) -> None:
     def _update_with(
         self,
         *,
-        value: ParamDataType,
+        value: ParameterDataTypeVar,
         raw_value: ParamRawDataType,
         timestamp: datetime | None = None,
     ) -> None:
@@ -187,7 +209,19 @@ def _timestamp_expired(self) -> bool:
             # parameter is still valid
             return False
 
-    def get(self, get_if_invalid: bool = True) -> ParamDataType:
+    @overload
+    def get(self, get_if_invalid: Literal[True]) -> ParameterDataTypeVar: ...
+
+    @overload
+    def get(self) -> ParameterDataTypeVar: ...
+
+    @overload
+    def get(self, get_if_invalid: Literal[False]) -> ParameterDataTypeVar | None: ...
+
+    @overload
+    def get(self, get_if_invalid: bool) -> ParameterDataTypeVar | None: ...
+
+    def get(self, get_if_invalid: bool = True) -> ParameterDataTypeVar | None:
         """
         Return cached value if time since get was less than ``max_val_age``,
         or the parameter was explicitly marked invalid.
@@ -246,7 +280,7 @@ def _construct_error_msg(self) -> str:
             )
         return error_msg
 
-    def __call__(self) -> ParamDataType:
+    def __call__(self) -> ParameterDataTypeVar:
         """
         Same as :meth:`get` but always call ``get`` on parameter if the
         cache is not valid

src/qcodes/parameters/delegate_parameter.py

@@ -1,19 +1,39 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Any
+from typing import TYPE_CHECKING, Any, Generic
+
+from typing_extensions import TypeVar
 
 from .parameter import Parameter
+from .parameter_base import InstrumentTypeVar_co, ParameterDataTypeVar
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
     from datetime import datetime
 
+    from qcodes.instrument import InstrumentBase
     from qcodes.validators.validators import Validator
 
-    from .parameter_base import ParamDataType, ParamRawDataType
-
-
-class DelegateParameter(Parameter):
+    from .parameter_base import (
+        ParamDataType,
+        ParamRawDataType,
+    )
+
+# Generic type variables for inner cache class
+# these need to be different variables such that both classes can be generic
+_local_ParameterDataTypeVar = TypeVar("_local_ParameterDataTypeVar", default=Any)
+_local_InstrumentTypeVar_co = TypeVar(
+    "_local_InstrumentTypeVar_co",
+    bound="InstrumentBase | None",
+    default="InstrumentBase | None",
+    covariant=True,
+)
+
+
+class DelegateParameter(
+    Parameter[ParameterDataTypeVar, InstrumentTypeVar_co],
+    Generic[ParameterDataTypeVar, InstrumentTypeVar_co],
+):
     """
     The :class:`.DelegateParameter` wraps a given `source` :class:`Parameter`.
     Setting/getting it results in a set/get of the source parameter with
@@ -51,8 +71,15 @@ class DelegateParameter(Parameter):
 
     """
 
-    class _DelegateCache:
-        def __init__(self, parameter: DelegateParameter):
+    class _DelegateCache(
+        Generic[_local_ParameterDataTypeVar, _local_InstrumentTypeVar_co]
+    ):
+        def __init__(
+            self,
+            parameter: DelegateParameter[
+                _local_ParameterDataTypeVar, _local_InstrumentTypeVar_co
+            ],
+        ):
             self._parameter = parameter
             self._marked_valid: bool = False
 
@@ -99,7 +126,7 @@ def invalidate(self) -> None:
             if self._parameter.source is not None:
                 self._parameter.source.cache.invalidate()
 
-        def get(self, get_if_invalid: bool = True) -> ParamDataType:
+        def get(self, get_if_invalid: bool = True) -> _local_ParameterDataTypeVar:
             if self._parameter.source is None:
                 raise TypeError(
                     "Cannot get the cache of a DelegateParameter that delegates to None"
@@ -108,7 +135,7 @@ def get(self, get_if_invalid: bool = True) -> ParamDataType:
                 self._parameter.source.cache.get(get_if_invalid=get_if_invalid)
             )
 
-        def set(self, value: ParamDataType) -> None:
+        def set(self, value: _local_ParameterDataTypeVar) -> None:
             if self._parameter.source is None:
                 raise TypeError(
                     "Cannot set the cache of a DelegateParameter that delegates to None"
@@ -128,7 +155,7 @@ def _set_from_raw_value(self, raw_value: ParamRawDataType) -> None:
         def _update_with(
             self,
             *,
-            value: ParamDataType,
+            value: _local_ParameterDataTypeVar,
             raw_value: ParamRawDataType,
             timestamp: datetime | None = None,
         ) -> None:
@@ -142,7 +169,7 @@ def _update_with(
             """
             pass
 
-        def __call__(self) -> ParamDataType:
+        def __call__(self) -> _local_ParameterDataTypeVar:
             return self.get(get_if_invalid=True)
 
     def __init__(
@@ -183,7 +210,9 @@ def __init__(
         # i.e. _SetParamContext overrides it
         self._settable = True
 
-        self.cache = self._DelegateCache(self)
+        self.cache = self._DelegateCache[ParameterDataTypeVar, InstrumentTypeVar_co](
+            self
+        )
         if initial_cache_value is not None:
             self.cache.set(initial_cache_value)
 

src/qcodes/parameters/multi_parameter.py

@@ -2,16 +2,13 @@
 
 import os
 from collections.abc import Iterator, Mapping, Sequence
-from typing import TYPE_CHECKING, Any
+from typing import Any, Generic
 
 import numpy as np
 
-from .parameter_base import ParameterBase
+from .parameter_base import InstrumentTypeVar_co, ParameterBase, ParameterDataTypeVar
 from .sequence_helpers import is_sequence_of
 
-if TYPE_CHECKING:
-    from qcodes.instrument import InstrumentBase
-
 try:
     from qcodes_loop.data.data_array import DataArray
 
@@ -50,7 +47,10 @@ def _is_nested_sequence_or_none(
     return True
 
 
-class MultiParameter(ParameterBase):
+class MultiParameter(
+    ParameterBase[ParameterDataTypeVar, InstrumentTypeVar_co],
+    Generic[ParameterDataTypeVar, InstrumentTypeVar_co],
+):
     """
     A gettable parameter that returns multiple values with separate names,
     each of arbitrary shape. Not necessarily part of an instrument.
@@ -141,7 +141,9 @@ def __init__(
         name: str,
         names: Sequence[str],
         shapes: Sequence[Sequence[int]],
-        instrument: InstrumentBase | None = None,
+        # mypy seems to be confused here. The bound and default for InstrumentTypeVar_co
+        # contains None but mypy will not allow it as a default as of v 1.19.0
+        instrument: InstrumentTypeVar_co = None,  # type: ignore[assignment]
         labels: Sequence[str] | None = None,
         units: Sequence[str] | None = None,
         setpoints: Sequence[Sequence[Any]] | None = None,

src/qcodes/parameters/parameter.py

@@ -6,10 +6,15 @@
 import logging
 import os
 from types import MethodType
-from typing import TYPE_CHECKING, Any, Literal
+from typing import TYPE_CHECKING, Any, Generic, Literal
 
 from .command import Command
-from .parameter_base import ParamDataType, ParameterBase, ParamRawDataType
+from .parameter_base import (
+    InstrumentTypeVar_co,
+    ParameterBase,
+    ParameterDataTypeVar,
+    ParamRawDataType,
+)
 from .sweep_values import SweepFixedValues
 
 if TYPE_CHECKING:
@@ -24,7 +29,10 @@
 log = logging.getLogger(__name__)
 
 
-class Parameter(ParameterBase):
+class Parameter(
+    ParameterBase[ParameterDataTypeVar, InstrumentTypeVar_co],
+    Generic[ParameterDataTypeVar, InstrumentTypeVar_co],
+):
     """
     A parameter represents a single degree of freedom. Most often,
     this is the standard parameter for Instruments, though it can also be
@@ -172,16 +180,18 @@ class Parameter(ParameterBase):
     def __init__(
         self,
         name: str,
-        instrument: InstrumentBase | None = None,
+        # mypy seems to be confused here. The bound and default for InstrumentTypeVar_co
+        # contains None but mypy will not allow None as a default as of v 1.19.0
+        instrument: InstrumentTypeVar_co = None,  # type: ignore[assignment]
         label: str | None = None,
         unit: str | None = None,
         get_cmd: str | Callable[..., Any] | Literal[False] | None = None,
         set_cmd: str | Callable[..., Any] | Literal[False] | None = False,
-        initial_value: float | str | None = None,
+        initial_value: ParameterDataTypeVar | None = None,
         max_val_age: float | None = None,
         vals: Validator[Any] | None = None,
         docstring: str | None = None,
-        initial_cache_value: float | str | None = None,
+        initial_cache_value: ParameterDataTypeVar | None = None,
         bind_to_instrument: bool = True,
         **kwargs: Any,
     ) -> None:
@@ -396,14 +406,16 @@ def __getitem__(self, keys: Any) -> SweepFixedValues:
         """
         return SweepFixedValues(self, keys)
 
-    def increment(self, value: ParamDataType) -> None:
+    def increment(self, value: ParameterDataTypeVar) -> None:
         """Increment the parameter with a value
 
         Args:
             value: Value to be added to the parameter.
 
         """
-        self.set(self.get() + value)
+        # this method only works with parameters that support addition
+        # however we don't currently enforce that via typing
+        self.set(self.get() + value)  # type: ignore[operator]
 
     def sweep(
         self,