Change the exception type when a context is not defined.

theano/sandbox/gpuarray/opt.py

@@ -17,7 +17,8 @@ from theano.scan_module import scan_utils, scan_op, scan_opt
 from theano.tensor.nnet.conv import ConvOp
 from theano.tests.breakpoint import PdbBreakpoint
 
-from .type import GpuArrayType, GpuArrayConstant, get_context
+from .type import (GpuArrayType, GpuArrayConstant, get_context,
+                   ContextNotDefined)
 from .basic_ops import (as_gpuarray_variable, infer_context_name,
                         host_from_gpu, GpuToGpu,
                         HostFromGpu, GpuFromHost,
@@ -177,7 +178,7 @@ class InputToGpuOptimizer(Optimizer):
             except TypeError:
                 # This could fail if the inputs are not TensorTypes
                 pass
-            except ValueError:
+            except ContextNotDefined:
                 # If there is no context tag and no default context
                 # then it stays on the CPU
                 if not hasattr(input.tag, 'context_name'):
@@ -255,7 +256,7 @@ def local_gpuaalloc2(node):
     """
     try:
         get_context(None)
-    except ValueError:
+    except ContextNotDefined:
         # If there is no default context then we do not perform the move here.
         return
     if (isinstance(node.op, tensor.Alloc) and

theano/sandbox/gpuarray/type.py

@@ -17,6 +17,10 @@ except ImportError:
 _context_reg = {}
 
 
+class ContextNotDefined(ValueError):
+    pass
+
+
 def reg_context(name, ctx):
     """
     Register a context by mapping it to a name.
@@ -56,7 +60,7 @@ def get_context(name):
 
     """
     if name not in _context_reg:
-        raise ValueError("context name %s not defined" % (name,))
+        raise ContextNotDefined("context name %s not defined" % (name,))
     return _context_reg[name]
 
 
@@ -72,7 +76,7 @@ def _name_for_ctx(ctx):
     for k, v in _context_reg:
         if v == ctx:
             return k
-        raise ValueError('context is not registered')
+        raise ContextNotDefined('context is not registered')
 
 
 # This is a private method for use by the tests only
@@ -479,7 +483,7 @@ def gpuarray_shared_constructor(value, name=None, strict=False,
 
     try:
         get_context(context_name)
-    except ValueError:
+    except ContextNotDefined:
         # Don't make this a hard error if we attempt to make a shared
         # variable while there is no default context.
         if context_name is None: