add optional validation to ValueType

* add optional parameter for ValueType: validator
used for checking, if a value meets a criteria (e.g. is dict)
+ InternalParameter, which is not exported and can hold any python value

Change-Id: If39a7a4a8019f2aa1a930e42cbef4fca59163b78
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/30787
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Alexander Zaft <a.zaft@fz-juelich.de>

frappy/datatypes.py

@@ -28,8 +28,8 @@
 import sys
 from base64 import b64decode, b64encode
 
-from frappy.errors import WrongTypeError, RangeError, \
-    ConfigError, ProgrammingError, ProtocolError, DiscouragedConversion
+from frappy.errors import ConfigError, DiscouragedConversion, \
+    ProgrammingError, ProtocolError, RangeError, WrongTypeError
 from frappy.lib import clamp, generalConfig
 from frappy.lib.enum import Enum
 from frappy.parse import Parser
@@ -1161,11 +1161,35 @@ class DataTypeType(DataType):
 
 
 class ValueType(DataType):
-    """validates any python value"""
+    """Can take any python value.
+
+    The optional (callable) validator can be used to restrict values to a
+    certain type.
+    For example using `ValueType(dict)` would ensure only values that can be
+    turned into a dictionary can be used in this instance, as the conversion
+    `dict(value)` is called for validation.
+
+    Notes:
+    The validator must either accept a value by returning it or the converted value,
+    or raise an error.
+    """
+    def __init__(self, validator=None):
+        super().__init__()
+        self.validator = validator
+
     def __call__(self, value):
-        """accepts any type -> no conversion"""
+        """accepts any type -> default is no conversion"""
+        if self.validator:
+            try:
+                return self.validator(value)
+            except Exception as e:
+                raise ConfigError('Validator %s raised %r for value %s' \
+                                           % (self.validator, e, value)) from e
         return value
 
+    def copy(self):
+        return ValueType(self.validator)
+
     def export_value(self, value):
         """if needed, reformat value for transport"""
         return value

frappy/params.py

@@ -163,7 +163,7 @@ class Parameter(Accessible):
         export=False, default=False)
     update_unchanged = Property(
         '''[internal] updates of unchanged values
-        
+
         - one of the values 'always', 'never', 'default'
           or the minimum time between updates of equal values [sec]''',
         OrType(FloatRange(0), EnumType(always=0, never=999999999, default=-1)),

test/test_datatypes.py

@@ -25,13 +25,12 @@
 # no fixtures needed
 import pytest
 
-from frappy.datatypes import ArrayOf, BLOBType, BoolType, \
-    CommandType, ConfigError, DataType, EnumType, FloatRange, \
-    IntRange, ProgrammingError, ScaledInteger, StatusType, \
-    StringType, StructOf, TextType, TupleOf, get_datatype, \
-    DiscouragedConversion
+from frappy.datatypes import ArrayOf, BLOBType, BoolType, CommandType, \
+    ConfigError, DataType, DiscouragedConversion, EnumType, FloatRange, \
+    IntRange, ProgrammingError, ScaledInteger, StatusType, StringType, \
+    StructOf, TextType, TupleOf, ValueType, get_datatype
+from frappy.errors import BadValueError, RangeError, WrongTypeError
 from frappy.lib import generalConfig
-from frappy.errors import WrongTypeError, RangeError, BadValueError
 
 
 def copytest(dt):
@@ -725,3 +724,36 @@ def test_main_unit(unit, dt):
     assert '$' in before
     assert before != after
     assert before.replace('$', unit) == after
+
+def ex_validator(i):
+    if i > 10:
+        raise RuntimeError('too large')
+    return i
+
+@pytest.mark.parametrize('validator, value, result', [
+    (dict, [('a', 1)], {'a': 1}),
+    (ex_validator, 5, 5),
+    # pylint: disable=unnecessary-lambda
+    (lambda x: dict(x), {'a': 1}, {'a': 1}),
+    # pylint: disable=unnecessary-lambda
+    (lambda i: ex_validator(i) * 3, 3, 9),
+])
+def test_value_type(validator, value, result):
+    t = ValueType()
+    tv = ValueType(validator)
+    assert t(value) == value
+    assert tv(value) == result
+
+
+@pytest.mark.parametrize('validator, value', [
+    (dict, 'strinput'),
+    (ex_validator, 20),
+    # pylint: disable=unnecessary-lambda
+    (lambda i: list(i), 1),
+])
+def test_value_type_rejecting(validator, value):
+    t = ValueType()
+    tv = ValueType(validator)
+    assert t(value) == value
+    with pytest.raises(ConfigError):
+        tv(value)