Separated casting functionality from Identity into a new Cast Op in

theano/scalar/basic.py

@@ -830,36 +830,45 @@ second = Second(transfer_type(1), name = 'second')
 
 
 class Identity(UnaryScalarOp):
-    def impl(self, x):
-        return getattr(numpy, self.output_types_preference.spec[0].dtype)(x)
+    def impl(self, input):
+        return input
     def c_code(self, node, name, (x, ), (z, ), sub):
         return "%(z)s = %(x)s;" % locals()
     def grad(self, (x, ), (gz, )):
         if x.type in grad_types:
-          return [cast(gz, x.type.dtype)]
+            return gz,
         else:
             return None,
-
-        #backport
-        #return gz if x.type in grad_types else None,
 identity = Identity(same_out, name = 'identity')
 
 #### CASTING OPERATIONS
+class Cast(UnaryScalarOp):
+    def __init__(self, o_type, name=None):
+        if not isinstance(o_type, Scalar):
+            raise TypeError(o_type)
+        super(Cast, self).__init__(specific_out(o_type), name=name)
+        self.o_type = o_type
+        self.ctor = getattr(numpy, o_type.dtype)
+    def impl(self, input):
+        return self.ctor(input)
+    def c_code(self, node, name, (x, ), (z, ), sub):
+        return "%(z)s = %(x)s;" % locals()
+    def grad(self, (x, ), (gz, )):
+        if x.type in grad_types:
+          return [cast(gz, x.type.dtype)]
+        else:
+          return None,
+
+convert_to_int8 = Cast(int8, name='convert_to_int8')
+convert_to_int16 = Cast(int16, name='convert_to_int16')
+convert_to_int32 = Cast(int32, name='convert_to_int32')
+convert_to_int64 = Cast(int64, name='convert_to_int64')
+convert_to_float32 = Cast(float32, name='convert_to_float32')
+convert_to_float64 = Cast(float64, name='convert_to_float64')
+convert_to_complex64 = Cast(complex64, name='convert_to_complex64')
+convert_to_complex128 = Cast(complex128, name='convert_to_complex128')
 
-convert_to_int8 = Identity(specific_out(int8), name='convert_to_int8')
-convert_to_int16 = Identity(specific_out(int16), name='convert_to_int16')
-convert_to_int32 = Identity(specific_out(int32), name='convert_to_int32')
-convert_to_int64 = Identity(specific_out(int64), name='convert_to_int64')
-convert_to_float32 = Identity(specific_out(float32), name='convert_to_float32')
-convert_to_float64 = Identity(specific_out(float64), name='convert_to_float64')
-convert_to_complex64 = Identity(specific_out(complex64), name='convert_to_complex64')
-convert_to_complex128 = Identity(specific_out(complex128), name='convert_to_complex128')
-
-def cast(t, dtype):
-    if t.type.dtype == dtype:
-        return t
-    """symbolically cast `t` to a Scalar of type `dtype`.""" 
-    mapping = {'int8': convert_to_int8,
+_cast_mapping = {'int8': convert_to_int8,
            'int16': convert_to_int16,
            'int32': convert_to_int32,
            'int64': convert_to_int64,
@@ -867,9 +876,14 @@ def cast(t, dtype):
            'float64': convert_to_float64,
            'complex64': convert_to_complex64,
            'complex128': convert_to_complex128}
-    if t.type.dtype.startswith('complex') and not dtype.startswith('complex'):
+def cast(x, dtype):
+    """Symbolically cast `x` to a Scalar of given `dtype`.""" 
+    _x = as_scalar(x)
+    if _x.type.dtype == dtype:
+        return _x
+    if _x.type.dtype.startswith('complex') and not dtype.startswith('complex'):
         raise TypeError('Casting from complex to real is ambiguous: consider real(), imag(), angle() or abs()')
-    return mapping[dtype](t)
+    return _cast_mapping[dtype](_x)
 
 class Abs(UnaryScalarOp):
     def make_node(self, x):