Unify all config parameter types

tests/test_config.py

-"""
-Test config options.
-"""
+"""Test config options."""
 import logging
 from unittest.mock import patch
 
+import pytest
+
+from theano import configparser
 from theano.configdefaults import default_blas_ldflags
 from theano.configparser import THEANO_FLAGS_DICT, AddConfigVar, ConfigParam
 
@@ -12,24 +13,23 @@ def test_invalid_default():
     # Ensure an invalid default value found in the Theano code only causes
     # a crash if it is not overridden by the user.
 
-    def filter(val):
+    def validate(val):
         if val == "invalid":
-            raise ValueError()
-        else:
-            return val
+            raise ValueError("Test-triggered")
 
-    try:
+    with pytest.raises(ValueError, match="Test-triggered"):
         # This should raise a ValueError because the default value is
         # invalid.
         AddConfigVar(
             "T_config.test_invalid_default_a",
             doc="unittest",
-            configparam=ConfigParam("invalid", filter=filter),
+            configparam=ConfigParam("invalid", validate=validate),
             in_c_key=False,
         )
-        raise AssertionError()
-    except ValueError:
-        pass
+
+    THEANO_FLAGS_DICT["T_config.test_invalid_default_b"] = "ok"
+    # This should succeed since we defined a proper value, even
+    # though the default was invalid.
 
     THEANO_FLAGS_DICT["T_config.test_invalid_default_b"] = "ok"
     # This should succeed since we defined a proper value, even
@@ -37,15 +37,14 @@ def test_invalid_default():
     AddConfigVar(
         "T_config.test_invalid_default_b",
         doc="unittest",
-        configparam=ConfigParam("invalid", filter=filter),
+        configparam=ConfigParam("invalid", validate=validate),
         in_c_key=False,
     )
 
+    # TODO We should remove these dummy options on test exit.
     # Check that the flag has been removed
     assert "T_config.test_invalid_default_b" not in THEANO_FLAGS_DICT
 
-    # TODO We should remove these dummy options on test exit.
-
 
 @patch("theano.configdefaults.try_blas_flag", return_value=None)
 @patch("theano.configdefaults.sys")
@@ -58,3 +57,50 @@ def test_default_blas_ldflags(sys_mock, try_blas_flag_mock, caplog):
             default_blas_ldflags()
 
     assert "install mkl with" in caplog.text
+
+
+def test_config_param_apply_and_validation():
+    cp = ConfigParam(
+        "TheDeFauLt",
+        apply=lambda v: v.lower(),
+        validate=lambda v: v in "thedefault,thesetting",
+        mutable=True,
+    )
+    assert cp.default == "TheDeFauLt"
+    assert not hasattr(cp, "val")
+
+    # can't assign invalid value
+    with pytest.raises(ValueError, match="Invalid value"):
+        cp.__set__("cls", "invalid")
+
+    assert not hasattr(cp, "val")
+
+    # effectivity of apply function
+    cp.__set__("cls", "THESETTING")
+    assert cp.val == "thesetting"
+
+    # respect the mutability
+    cp._mutable = False
+    with pytest.raises(Exception, match="Can't change"):
+        cp.__set__("cls", "THEDEFAULT")
+
+
+def test_config_types_bool():
+    valids = {
+        True: ["1", 1, True, "true", "True"],
+        False: ["0", 0, False, "false", "False"],
+    }
+
+    param = configparser.BoolParam(None)
+
+    assert isinstance(param, configparser.ConfigParam)
+    assert param.default is None
+
+    for outcome, inputs in valids.items():
+        for input in inputs:
+            applied = param.apply(input)
+            assert applied == outcome
+            assert param.validate(applied) is not False
+
+    with pytest.raises(ValueError, match="Invalid value"):
+        param.apply("notabool")

theano/configdefaults.py

@@ -17,6 +17,7 @@ from theano.configparser import (
     AddConfigVar,
     BoolParam,
     ConfigParam,
+    DeviceParam,
     EnumStr,
     FloatParam,
     IntParam,
@@ -109,38 +110,6 @@ AddConfigVar(
 # gpuX mean use the gpu number X.
 
 
-class DeviceParam(ConfigParam):
-    def __init__(self, default, *options, **kwargs):
-        self.default = default
-
-        def filter(val):
-            if (
-                val == self.default
-                or val.startswith("opencl")
-                or val.startswith("cuda")
-            ):
-                return val
-            elif val.startswith("gpu"):
-                raise ValueError(
-                    "You are tring to use the old GPU back-end. "
-                    "It was removed from Theano. Use device=cuda* now. "
-                    "See https://github.com/Theano/Theano/wiki/Converting-to-the-new-gpu-back-end%28gpuarray%29 "
-                    "for more information."
-                )
-            else:
-                raise ValueError(
-                    'Invalid value ("{val}") for configuration '
-                    'variable "{self.fullname}". Valid options start with '
-                    'one of "cpu", "opencl" or "cuda".'
-                )
-
-        over = kwargs.get("allow_override", True)
-        super().__init__(default, filter, over)
-
-    def __str__(self):
-        return f"{self.fullname} ({self.default}, opencl*, cuda*) "
-
-
 AddConfigVar(
     "device",
     (
@@ -148,7 +117,7 @@ AddConfigVar(
         "default to try to move computation to the GPU. Do not use upper case"
         "letters, only lower case even if NVIDIA uses capital letters."
     ),
-    DeviceParam("cpu", allow_override=False),
+    DeviceParam("cpu", mutable=False),
     in_c_key=False,
 )
 
@@ -160,14 +129,14 @@ AddConfigVar(
         "nor shared variables, to the specified GPU. "
         "It can be used to run GPU-specific tests on a particular GPU."
     ),
-    DeviceParam("", allow_override=False),
+    DeviceParam("", mutable=False),
     in_c_key=False,
 )
 
 AddConfigVar(
     "force_device",
     "Raise an error if we can't use the specified device",
-    BoolParam(False, allow_override=False),
+    BoolParam(False, mutable=False),
     in_c_key=False,
 )
 
@@ -205,7 +174,7 @@ class ContextsParam(ConfigParam):
                     raise ValueError(f"Cannot use {s[0]} as context name")
             return val
 
-        ConfigParam.__init__(self, "", filter, False)
+        ConfigParam.__init__(self, "", apply=filter, mutable=False)
 
 
 AddConfigVar(
@@ -226,23 +195,7 @@ AddConfigVar(
 AddConfigVar(
     "print_active_device",
     "Print active device at when the GPU device is initialized.",
-    BoolParam(True, allow_override=False),
-    in_c_key=False,
-)
-
-
-def deprecated_gpuarray_sync(val):
-    if val:
-        raise RuntimeError(
-            "Flag gpuarray.sync is deprecated and will be removed in next Theano release."
-        )
-    return False
-
-
-AddConfigVar(
-    "gpuarray.sync",
-    """This flag is deprecated and will be removed in next Theano release.""",
-    ConfigParam(False, allow_override=False, filter=deprecated_gpuarray_sync),
+    BoolParam(True, mutable=False),
     in_c_key=False,
 )
 
@@ -253,7 +206,7 @@ AddConfigVar(
              preallocates that fraction of the total GPU memory.  If 1
              or greater it will preallocate that amount of memory (in
              megabytes).""",
-    FloatParam(0, allow_override=False),
+    FloatParam(0, mutable=False),
     in_c_key=False,
 )
 
@@ -323,62 +276,6 @@ AddConfigVar(
 )
 
 
-def safe_no_dnn_workmem(workmem):
-    """
-    Make sure the user is not attempting to use dnn.conv.workmem`.
-    """
-    if workmem:
-        raise RuntimeError(
-            "The option `dnn.conv.workmem` has been removed and should "
-            "not be used anymore. Please use the option "
-            "`dnn.conv.algo_fwd` instead."
-        )
-    return True
-
-
-AddConfigVar(
-    "dnn.conv.workmem",
-    "This flag is deprecated; use dnn.conv.algo_fwd.",
-    ConfigParam("", allow_override=False, filter=safe_no_dnn_workmem),
-    in_c_key=False,
-)
-
-
-def safe_no_dnn_workmem_bwd(workmem):
-    """
-    Make sure the user is not attempting to use dnn.conv.workmem_bwd`.
-    """
-    if workmem:
-        raise RuntimeError(
-            "The option `dnn.conv.workmem_bwd` has been removed and "
-            "should not be used anymore. Please use the options "
-            "`dnn.conv.algo_bwd_filter` and `dnn.conv.algo_bwd_data` instead."
-        )
-    return True
-
-
-AddConfigVar(
-    "dnn.conv.workmem_bwd",
-    "This flag is deprecated; use `dnn.conv.algo_bwd_filter` "
-    "and `dnn.conv.algo_bwd_data` instead.",
-    ConfigParam("", allow_override=False, filter=safe_no_dnn_workmem_bwd),
-    in_c_key=False,
-)
-
-
-def safe_no_dnn_algo_bwd(algo):
-    """
-    Make sure the user is not attempting to use dnn.conv.algo_bwd`.
-    """
-    if algo:
-        raise RuntimeError(
-            "The option `dnn.conv.algo_bwd` has been removed and "
-            "should not be used anymore. Please use the options "
-            "`dnn.conv.algo_bwd_filter` and `dnn.conv.algo_bwd_data` instead."
-        )
-    return True
-
-
 # Those are the options provided by Theano to choose algorithms at runtime.
 SUPPORTED_DNN_CONV_ALGO_RUNTIME = (
     "guess_once",
@@ -425,14 +322,6 @@ SUPPORTED_DNN_CONV_PRECISION = (
     "float64",
 )
 
-AddConfigVar(
-    "dnn.conv.algo_bwd",
-    "This flag is deprecated; use dnn.conv.algo_bwd_data and "
-    "dnn.conv.algo_bwd_filter.",
-    ConfigParam("", allow_override=False, filter=safe_no_dnn_algo_bwd),
-    in_c_key=False,
-)
-
 AddConfigVar(
     "dnn.conv.algo_fwd",
     "Default implementation to use for cuDNN forward convolution.",
@@ -569,7 +458,7 @@ AddConfigVar(
 AddConfigVar(
     "assert_no_cpu_op",
     "Raise an error/warning if there is a CPU op in the computational graph.",
-    EnumStr("ignore", "warn", "raise", "pdb", allow_override=True),
+    EnumStr("ignore", "warn", "raise", "pdb", mutable=True),
     in_c_key=False,
 )
 
@@ -604,7 +493,10 @@ def filter_mode(val):
 
 
 AddConfigVar(
-    "mode", "Default compilation mode", ConfigParam("Mode", filter_mode), in_c_key=False
+    "mode",
+    "Default compilation mode",
+    ConfigParam("Mode", apply=filter_mode),
+    in_c_key=False,
 )
 
 param = "g++"
@@ -675,7 +567,7 @@ AddConfigVar(
     " supported, but supporting additional compilers should not be "
     "too difficult. "
     "If it is empty, no C++ code is compiled.",
-    StrParam(param, is_valid=warn_cxx),
+    StrParam(param, validate=warn_cxx),
     in_c_key=False,
 )
 del param
@@ -775,7 +667,7 @@ AddConfigVar(
 AddConfigVar(
     "tensor.cmp_sloppy",
     "Relax tensor._allclose (0) not at all, (1) a bit, (2) more",
-    IntParam(0, lambda i: i in (0, 1, 2), allow_override=False),
+    IntParam(0, lambda i: i in (0, 1, 2), mutable=False),
     in_c_key=False,
 )
 
@@ -864,9 +756,7 @@ AddConfigVar(
         "by the following flags: seterr_divide, seterr_over, "
         "seterr_under and seterr_invalid.",
     ),
-    EnumStr(
-        "ignore", "warn", "raise", "call", "print", "log", "None", allow_override=False
-    ),
+    EnumStr("ignore", "warn", "raise", "call", "print", "log", "None", mutable=False),
     in_c_key=False,
 )
 
@@ -876,9 +766,7 @@ AddConfigVar(
         "Sets numpy's behavior for division by zero, see numpy.seterr. "
         "'None' means using the default, defined by numpy.seterr_all."
     ),
-    EnumStr(
-        "None", "ignore", "warn", "raise", "call", "print", "log", allow_override=False
-    ),
+    EnumStr("None", "ignore", "warn", "raise", "call", "print", "log", mutable=False),
     in_c_key=False,
 )
 
@@ -889,9 +777,7 @@ AddConfigVar(
         "see numpy.seterr. "
         "'None' means using the default, defined by numpy.seterr_all."
     ),
-    EnumStr(
-        "None", "ignore", "warn", "raise", "call", "print", "log", allow_override=False
-    ),
+    EnumStr("None", "ignore", "warn", "raise", "call", "print", "log", mutable=False),
     in_c_key=False,
 )
 
@@ -902,9 +788,7 @@ AddConfigVar(
         "see numpy.seterr. "
         "'None' means using the default, defined by numpy.seterr_all."
     ),
-    EnumStr(
-        "None", "ignore", "warn", "raise", "call", "print", "log", allow_override=False
-    ),
+    EnumStr("None", "ignore", "warn", "raise", "call", "print", "log", mutable=False),
     in_c_key=False,
 )
 
@@ -915,9 +799,7 @@ AddConfigVar(
         "see numpy.seterr. "
         "'None' means using the default, defined by numpy.seterr_all."
     ),
-    EnumStr(
-        "None", "ignore", "warn", "raise", "call", "print", "log", allow_override=False
-    ),
+    EnumStr("None", "ignore", "warn", "raise", "call", "print", "log", mutable=False),
     in_c_key=False,
 )
 
@@ -955,7 +837,7 @@ AddConfigVar(
         "1.0.3",
         "1.0.4",
         "1.0.5",
-        allow_override=False,
+        mutable=False,
     ),
     in_c_key=False,
 )
@@ -1166,7 +1048,7 @@ AddConfigVar(
 AddConfigVar(
     "reoptimize_unpickled_function",
     "Re-optimize the graph when a theano function is unpickled from the disk.",
-    BoolParam(False, allow_override=True),
+    BoolParam(False, mutable=True),
     in_c_key=False,
 )
 
@@ -1280,7 +1162,7 @@ AddConfigVar(
     "unittests.rseed",
     "Seed to use for randomized unit tests. "
     "Special value 'random' means using a seed of None.",
-    StrParam(666, is_valid=good_seed_param),
+    StrParam(666, validate=good_seed_param),
     in_c_key=False,
 )
 
@@ -1318,7 +1200,7 @@ AddConfigVar(
         "When using the default mode, we will remove optimizer with "
         "these tags. Separate tags with ':'."
     ),
-    StrParam("", allow_override=False),
+    StrParam("", mutable=False),
     in_c_key=False,
 )
 
@@ -1328,7 +1210,7 @@ AddConfigVar(
         "When using the default mode, we will add optimizer with "
         "these tags. Separate tags with ':'."
     ),
-    StrParam("", allow_override=False),
+    StrParam("", mutable=False),
     in_c_key=False,
 )
 
@@ -1338,7 +1220,7 @@ AddConfigVar(
         "When using the default mode, we will require optimizer with "
         "these tags. Separate tags with ':'."
     ),
-    StrParam("", allow_override=False),
+    StrParam("", mutable=False),
     in_c_key=False,
 )
 
@@ -1423,7 +1305,7 @@ AddConfigVar(
         '"wrong_size" (larger and smaller dimensions), and '
         '"ALL" (all of the above).'
     ),
-    StrParam("", is_valid=is_valid_check_preallocated_output_param),
+    StrParam("", validate=is_valid_check_preallocated_output_param),
     in_c_key=False,
 )
 
@@ -1565,7 +1447,7 @@ AddConfigVar(
 AddConfigVar(
     "cmodule.preload_cache",
     "If set to True, will preload the C module cache at import time",
-    BoolParam(False, allow_override=False),
+    BoolParam(False, mutable=False),
     in_c_key=False,
 )
 
@@ -1573,7 +1455,7 @@ AddConfigVar(
     "cmodule.age_thresh_use",
     "In seconds. The time after which " "Theano won't reuse a compile c module.",
     # 24 days
-    IntParam(60 * 60 * 24 * 24, allow_override=False),
+    IntParam(60 * 60 * 24 * 24, mutable=False),
     in_c_key=False,
 )
 
@@ -1979,7 +1861,7 @@ AddConfigVar(
     " auto detect if lazy evaluation is needed and use the appropriate"
     " version. If lazy is True/False, force the version used between"
     " Loop/LoopGC and Stack.",
-    ConfigParam("None", filter_vm_lazy),
+    ConfigParam("None", apply=filter_vm_lazy),
     in_c_key=False,
 )
 
@@ -2012,7 +1894,7 @@ AddConfigVar(
     " Generates error if not True. Use"
     " optimizer_excluding=local_alloc_elemwise"
     " to dsiable.",
-    theano.configparser.BoolParam(True, is_valid=lambda x: x),
+    theano.configparser.BoolParam(True),
     in_c_key=False,
 )
 
@@ -2049,7 +1931,7 @@ AddConfigVar(
 AddConfigVar(
     "compile.wait",
     """Time to wait before retrying to acquire the compile lock.""",
-    IntParam(5, lambda i: i > 0, allow_override=False),
+    IntParam(5, validate=lambda i: i > 0, mutable=False),
     in_c_key=False,
 )
 
@@ -2091,7 +1973,7 @@ override an existing lock. An override only happens when the existing
 lock is held by the same owner *and* has not been 'refreshed' by this
 owner for more than this period. Refreshes are done every half timeout
 period for running processes.""",
-    IntParam(_timeout_default, lambda i: i >= 0, allow_override=False),
+    IntParam(_timeout_default, validate=lambda i: i >= 0, mutable=False),
     in_c_key=False,
 )
 
@@ -2240,7 +2122,7 @@ AddConfigVar(
              """
         )
     ),
-    StrParam(default_compiledir_format, allow_override=False),
+    StrParam(default_compiledir_format, mutable=False),
     in_c_key=False,
 )
 
@@ -2331,9 +2213,7 @@ else:
 AddConfigVar(
     "base_compiledir",
     "platform-independent root directory for compiled modules",
-    ConfigParam(
-        default_base_compiledir, filter=filter_base_compiledir, allow_override=False
-    ),
+    ConfigParam(default_base_compiledir, apply=filter_base_compiledir, mutable=False),
     in_c_key=False,
 )
 
@@ -2345,7 +2225,7 @@ def default_compiledir():
 AddConfigVar(
     "compiledir",
     "platform-dependent cache directory for compiled modules",
-    ConfigParam(default_compiledir, filter=filter_compiledir, allow_override=False),
+    ConfigParam(default_compiledir, apply=filter_compiledir, mutable=False),
     in_c_key=False,
 )
 
@@ -2354,8 +2234,8 @@ AddConfigVar(
     "Directory to cache pre-compiled kernels for the gpuarray backend.",
     ConfigParam(
         lambda: os.path.join(config.compiledir, "gpuarray_kernels"),
-        filter=filter_base_compiledir,
-        allow_override=False,
+        apply=filter_base_compiledir,
+        mutable=False,
     ),
     in_c_key=False,
 )
@@ -2365,7 +2245,7 @@ AddConfigVar(
     "Directory which contains the root of Baidu CTC library. It is assumed \
     that the compiled library is either inside the build, lib or lib64 \
     subdirectory, and the header inside the include directory.",
-    StrParam("", allow_override=False),
+    StrParam("", mutable=False),
     in_c_key=False,
 )
 

theano/configparser.py

@@ -4,6 +4,7 @@ import logging
 import os
 import shlex
 import sys
+import typing
 import warnings
 from functools import wraps
 from io import StringIO
@@ -317,24 +318,86 @@ def AddConfigVar(name, doc, configparam, root=config, in_c_key=True):
 
 
 class ConfigParam:
-    def __init__(self, default, filter=None, allow_override=True):
+    """Base class of all kinds of configuration parameters.
+
+    A ConfigParam has not only default values and configurable mutability, but
+    also documentation text, as well as filtering and validation routines
+    that can be context-dependent.
+    """
+
+    def __init__(
+        self,
+        default: typing.Union[object, typing.Callable[[object], object]],
+        *,
+        apply: typing.Optional[typing.Callable[[object], object]] = None,
+        validate: typing.Optional[typing.Callable[[object], bool]] = None,
+        mutable: bool = True,
+    ):
         """
-        If allow_override is False, we can't change the value after the import
-        of Theano. So the value should be the same during all the execution.
+        Represents a configuration parameter and its associated casting and validation logic.
+
+        Parameters
+        ----------
+        default : object or callable
+            A default value, or function that returns a default value for this parameter.
+        apply : callable, optional
+            Callable that applies a modification to an input value during assignment.
+            Typical use cases: type casting or expansion of '~' to user home directory.
+        validate : callable, optional
+            A callable that validates the parameter value during assignment.
+            It may raise an (informative!) exception itself, or simply return True/False.
+            For example to check the availability of a path, device or to restrict a float into a range.
+        mutable : bool
+            If mutable is False, the value of this config settings can not be changed at runtime.
         """
-        self.default = default
-        self.filter = filter
-        self.allow_override = allow_override
+        self._default = default
+        self._apply = apply
+        self._validate = validate
+        self._mutable = mutable
         self.is_default = True
-        # N.B. --
-        # self.fullname  # set by AddConfigVar
-        # self.doc       # set by AddConfigVar
+        # set by AddConfigVar:
+        self.fullname = None
+        self.doc = None
 
         # Note that we do not call `self.filter` on the default value: this
         # will be done automatically in AddConfigVar, potentially with a
         # more appropriate user-provided default value.
         # Calling `filter` here may actually be harmful if the default value is
         # invalid and causes a crash or has unwanted side effects.
+        super().__init__()
+
+    @property
+    def default(self):
+        return self._default
+
+    @property
+    def mutable(self) -> bool:
+        return self._mutable
+
+    def apply(self, value):
+        """Applies modifications to a parameter value during assignment.
+
+        Typical use cases are casting or the subsitution of '~' with the user home directory.
+        """
+        if callable(self._apply):
+            return self._apply(value)
+        return value
+
+    def validate(self, value) -> None:
+        """Validates that a parameter values falls into a supported set or range.
+
+        Raises
+        ------
+        ValueError
+            when the validation turns out negative
+        """
+        if not callable(self._validate):
+            return True
+        if self._validate(value) is False:
+            raise ValueError(
+                f"Invalid value ({value}) for configuration variable '{self.fullname}'."
+            )
+        return True
 
     def __get__(self, cls, type_, delete_key=False):
         if cls is None:
@@ -349,106 +412,105 @@ class ConfigParam:
                 else:
                     val_str = self.default
             self.__set__(cls, val_str)
-        # print "RVAL", self.val
         return self.val
 
     def __set__(self, cls, val):
-        if not self.allow_override and hasattr(self, "val"):
+        if not self.mutable and hasattr(self, "val"):
             raise Exception(
-                "Can't change the value of this config parameter "
-                "after initialization!"
+                "Can't change the value of {self.fullname} config parameter after initialization!"
             )
-        # print "SETTING PARAM", self.fullname,(cls), val
-        if self.filter:
-            self.val = self.filter(val)
-        else:
-            self.val = val
+        applied = self.apply(val)
+        self.validate(applied)
+        self.val = applied
 
 
 class EnumStr(ConfigParam):
     def __init__(self, default, *options, **kwargs):
-        self.default = default
-        self.all = (default,) + options
+        self.all = {default, *options}
 
         # All options should be strings
         for val in self.all:
             if not isinstance(val, str):
-                raise ValueError(
-                    "Valid values for an EnumStr parameter " "should be strings",
-                    val,
-                    type(val),
-                )
-
-        convert = kwargs.get("convert", None)
-
-        def filter(val):
-            if convert:
-                val = convert(val)
-            if val in self.all:
-                return val
-            else:
-                raise ValueError(
-                    f'Invalid value ("{val}") for configuration variable "{self.fullname}". '
-                    f"Valid options are {self.all}"
-                )
+                raise ValueError(f"Non-str value '{val}' for an EnumStr parameter.")
+        super().__init__(
+            default, apply=self._apply, mutable=kwargs.get("mutable", True)
+        )
 
-        over = kwargs.get("allow_override", True)
-        super().__init__(default, filter, over)
+    def _apply(self, val):
+        if val in self.all:
+            return val
+        else:
+            raise ValueError(
+                f'Invalid value ("{val}") for configuration variable "{self.fullname}". '
+                f"Valid options are {self.all}"
+            )
 
     def __str__(self):
         return f"{self.fullname} ({self.all}) "
 
 
 class TypedParam(ConfigParam):
-    def __init__(self, default, mytype, is_valid=None, allow_override=True):
-        self.mytype = mytype
-
-        def filter(val):
-            cast_val = mytype(val)
-            if callable(is_valid):
-                if is_valid(cast_val):
-                    return cast_val
-                else:
-                    raise ValueError(
-                        f"Invalid value ({val}) for configuration variable "
-                        f'"{self.fullname}".'
-                    )
-            return cast_val
-
-        super().__init__(default, filter, allow_override=allow_override)
-
     def __str__(self):
-        return f"{self.fullname} ({self.mytype}) "
+        # The "_apply" callable is the type itself.
+        return f"{self.fullname} ({self._apply}) "
 
 
-def StrParam(default, is_valid=None, allow_override=True):
-    return TypedParam(default, str, is_valid, allow_override=allow_override)
+class StrParam(TypedParam):
+    def __init__(self, default, validate=None, mutable=True):
+        super().__init__(default, apply=str, validate=validate, mutable=mutable)
 
 
-def IntParam(default, is_valid=None, allow_override=True):
-    return TypedParam(default, int, is_valid, allow_override=allow_override)
+class IntParam(TypedParam):
+    def __init__(self, default, validate=None, mutable=True):
+        super().__init__(default, apply=int, validate=validate, mutable=mutable)
 
 
-def FloatParam(default, is_valid=None, allow_override=True):
-    return TypedParam(default, float, is_valid, allow_override=allow_override)
+class FloatParam(TypedParam):
+    def __init__(self, default, validate=None, mutable=True):
+        super().__init__(default, apply=float, validate=validate, mutable=mutable)
 
 
-def BoolParam(default, is_valid=None, allow_override=True):
-    # see comment at the beginning of this file.
+class BoolParam(TypedParam):
+    """A boolean parameter that may be initialized from any of the following:
+    False, 0, "false", "False", "0"
+    True, 1, "true", "True", "1"
+    """
+
+    def __init__(self, default, validate=None, mutable=True):
+        super().__init__(default, apply=self._apply, validate=validate, mutable=mutable)
 
-    def booltype(s):
-        if s in ["False", "false", "0", False]:
+    def _apply(self, value):
+        if value in {False, 0, "false", "False", "0"}:
             return False
-        elif s in ["True", "true", "1", True]:
+        elif value in {True, 1, "true", "True", "1"}:
             return True
+        raise ValueError(
+            f"Invalid value ({value}) for configuration variable '{self.fullname}'."
+        )
 
-    def is_valid_bool(s):
-        if s in ["False", "false", "0", "True", "true", "1", False, True]:
-            return True
-        else:
-            return False
 
-    if is_valid is None:
-        is_valid = is_valid_bool
+class DeviceParam(ConfigParam):
+    def __init__(self, default, *options, **kwargs):
+        super().__init__(
+            default, apply=self._apply, mutable=kwargs.get("mutable", True)
+        )
 
-    return TypedParam(default, booltype, is_valid, allow_override=allow_override)
+    def _apply(self, val):
+        if val == self.default or val.startswith("opencl") or val.startswith("cuda"):
+            return val
+        elif val.startswith("gpu"):
+            raise ValueError(
+                "You are tring to use the old GPU back-end. "
+                "It was removed from Theano. Use device=cuda* now. "
+                "See https://github.com/Theano/Theano/wiki/Converting-to-the-new-gpu-back-end%28gpuarray%29 "
+                "for more information."
+            )
+        else:
+            raise ValueError(
+                'Invalid value ("{val}") for configuration '
+                'variable "{self.fullname}". Valid options start with '
+                'one of "cpu", "opencl" or "cuda".'
+            )
+
+    def __str__(self):
+        return f"{self.fullname} ({self.default}, opencl*, cuda*) "