fix failures from voluptuous update

Mostly these have to do with validation of default inputs.

Also, alecthomas/voluptuous#397, which I assume is a bug

docs/grading_math/sampling.md

@@ -91,8 +91,8 @@ Sample real matrices of a specific shape and norm. (`RealMatrices` uses the Frob
 >>> sampler = RealMatrices(shape=[3, 2], norm=[5, 10])
 >>> # the default is shape=[2, 2] and norm=[1, 5]
 >>> default_sampler = RealMatrices()
->>> default_sampler
-RealMatrices({'norm': [1, 5], 'shape': (2, 2)})
+>>> default_sampler == RealMatrices(shape=[2, 2], norm=[1, 5])
+True
 
 ```
 

mitxgraders/formulagrader/formulagrader.py

@@ -947,8 +947,8 @@ def schema_config(self):
             Required('user_functions', default={}): {Extra: is_callable},
             Required('tolerance', default='5%'): Any(PercentageString, NonNegative(Number)),
             Required('samples', default=1): 1,
-            Required('variables', default=[]): [],
-            Required('numbered_vars', default=[]): [],
+            Required('variables', default=[]): All(Length(max=0), []),
+            Required('numbered_vars', default=[]): All(Length(max=0), []),
             Required('sample_from', default={}): {},
             Required('failable_evals', default=0): 0
         })

mitxgraders/formulagrader/matrixgrader.py

@@ -8,7 +8,7 @@
 from voluptuous import Required, Any
 from mitxgraders.exceptions import InputTypeError
 from mitxgraders.formulagrader.formulagrader import FormulaGrader
-from mitxgraders.helpers.validatorfuncs import NonNegative
+from mitxgraders.helpers.validatorfuncs import NonNegative, Nullable
 from mitxgraders.helpers.calc import MathArray, within_tolerance, identity
 from mitxgraders.helpers.calc.exceptions import (
     MathArrayShapeError as ShapeError, MathArrayError, DomainError, ArgumentShapeError)
@@ -68,8 +68,8 @@ class MatrixGrader(FormulaGrader):
     def schema_config(self):
         schema = super(MatrixGrader, self).schema_config
         return schema.extend({
-            Required('identity_dim', default=None): NonNegative(int),
-            Required('max_array_dim', default=1): NonNegative(int),
+            Required('identity_dim', default=None): Nullable(NonNegative(int)),
+            Required('max_array_dim', default=1): Nullable(NonNegative(int)),
             Required('negative_powers', default=True): bool,
             Required('shape_errors', default=True): bool,
             Required('suppress_matrix_messages', default=False): bool,

mitxgraders/helpers/calc/specify_domain.py

@@ -6,7 +6,7 @@
 """
 from numbers import Number
 from voluptuous import Schema, Invalid, Required, Any
-from mitxgraders.helpers.validatorfuncs import is_shape_specification
+from mitxgraders.helpers.validatorfuncs import is_shape_specification, Nullable
 from mitxgraders.baseclasses import ObjectWithSchema
 from mitxgraders.helpers.calc.exceptions import ArgumentShapeError, ArgumentError
 from mitxgraders.helpers.calc.math_array import (
@@ -189,7 +189,7 @@ class SpecifyDomain(ObjectWithSchema):
         Required('input_shapes'): [Schema(
             Any(is_shape_specification(), 'square')
         )],
-        Required('display_name', default=None): str
+        Required('display_name', default=None): Nullable(str)
     })
 
     def __init__(self, config=None, **kwargs):

mitxgraders/helpers/validatorfuncs.py

@@ -347,3 +347,9 @@ def is_shape_specification(min_dim=1, max_dim=None):
         ),
         Length(min=min_dim, max=max_dim),
     )
+
+def Nullable(schema):
+    """
+    Indicates that a value could be None or satisfy schema.
+    """
+    return Any(None, schema)

tests/formulagrader/test_formulagrader.py

@@ -660,15 +660,15 @@ def test_ng_config():
             samples=2
         )
 
-    expect = "not a valid value for dictionary value @ data\['variables'\]. Got \['x'\]"
+    expect = "length of value must be at most 0 for dictionary value @ data\['variables'\]. Got \['x'\]"
     with raises(Error, match=expect):
         NumericalGrader(
             answers="1",
             variables=["x"]
         )
 
-    expect = "not a valid value for dictionary value @ data\['sample_from'\]. " + \
-             "Got {'x': RealInterval\({'start': 1, 'stop': 5}\)}"
+    expect = ("extra keys not allowed @ data\['sample_from'\]\['x'\]. Got "
+              "RealInterval\({'start': 1, 'stop': 5}\)")
     with raises(Error, match=expect):
         NumericalGrader(
             answers="1",