Merge branch 'expressive_errors' into 'NIFTy_5'

More expressive error messages for domain checks.

See merge request ift/nifty-dev!121

nifty5/operators/linear_operator.py

@@ -259,5 +259,4 @@ class LinearOperator(Operator):
 
     def _check_input(self, x, mode):
         self._check_mode(mode)
-        if self._dom(mode) != x.domain:
-            raise ValueError("The operator's and field's domains don't match.")
+        self._check_domain_equality(self._dom(mode), x.domain)

nifty5/operators/mask_operator.py

@@ -32,6 +32,15 @@ from .linear_operator import LinearOperator
 # collect the unstructured Fields.
 class MaskOperator(LinearOperator):
     def __init__(self, mask):
+        """Implementation of a mask response
+
+        This operator takes a field, applies a mask and returns the values of
+        the field in a UnstructuredDomain. It can be used as response operator.
+
+        Parameters
+        ----------
+        mask : Field
+        """
         if not isinstance(mask, Field):
             raise TypeError
 

nifty5/operators/operator.py

@@ -23,6 +23,17 @@ class Operator(NiftyMetaBase()):
             The domain on which the Operator's output Field lives."""
         return self._target
 
+    @staticmethod
+    def _check_domain_equality(dom_op, dom_field):
+        if dom_op != dom_field:
+            s = "The operator's and field's domains don't match."
+            from ..domain_tuple import DomainTuple
+            from ..multi_domain import MultiDomain
+            if not isinstance(dom_op, [DomainTuple, MultiDomain]):
+                s += " Your operator's domain is neither a `DomainTuple`" \
+                     " nor a `MultiDomain`."
+            raise ValueError(s)
+
     def scale(self, factor):
         if factor == 1:
             return self
@@ -66,8 +77,7 @@ class Operator(NiftyMetaBase()):
     def _check_input(self, x):
         from ..linearization import Linearization
         d = x.target if isinstance(x, Linearization) else x.domain
-        if self._domain != d:
-            raise ValueError("The operator's and field's domains don't match.")
+        self._check_domain_equality(self._domain, d)
 
     def __call__(self, x):
         if isinstance(x, Operator):