Revised version of infer_shape for theano that takes into consideration the

theano/tensor/basic.py

@@ -2835,31 +2835,21 @@ class Subtensor(Op):
         assert len(xshp) == node.inputs[0].ndim
         outshp = []
         actual_idx_list = list(get_idx_list(node.inputs, self.idx_list))
-        padded = actual_idx_list + [slice(None, None, None)] * (len(xshp) - len(self.idx_list))
+        padded = ( actual_idx_list +
+                  [slice(None, None, None)]*(len(xshp)-len(self.idx_list)))
         i = 0
-        shape_i = node.env.shape_feature.shape_i
         for idx, xl in zip(padded, xshp):
             if isinstance(idx, slice):
                 # If it is the default (None, None, None) slice, or a variant,
                 # the shape will be xl
-                if (idx.start is None or idx.start == 0)\
-                    and (idx.stop is None or idx.stop == sys.maxint)\
-                    and (idx.step is None or abs(idx.step) == 1):
+                if ( (idx.start in [None, 0])
+                    and (idx.stop in [None, sys.maxint])
+                    and (idx.step is None or idx.step == 1) ):
                     outshp.append(xl)
                 else:
                     cnf = get_canonical_form_slice(idx, xl)
-                    if cnf[0].stop not in [None, sys.maxint]:
-                        length = cnf[0].stop
-                    else:
-                        length = xl
-                    if cnf[0].start not in [None,0]:
-                        length = length - cnf[0].start
-                        length = switch(lt(length,0), 0, length)
-                    if cnf[0].step not in [None, 1]:
-                        # any more elegant way of doing this??
-                        length = cast(
-                            ceil(length / cast(cnf[0].step,'float32')),'int64')
-
+                    length = (cnf[0].stop - cnf[0].start -1)/cnf[0].step + 1
+                    length = switch(lt(length,0), 0, length)
                     outshp.append(length)
                 i += 1
             else: