warn about interface change.

NEWS_DEV.txt

@@ -13,6 +13,9 @@ Done up to PR 1608
 
 * https://github.com/Theano/Theano/pull/1591 # need info
 
+Interface change:
+ - theano.tensor.signal.conv2d(2d,2d) output 2d answer. (Frederic B., reported by Alexander Izvorski)
+
 
 Theano Development version
 ==========================

theano/configdefaults.py

@@ -400,6 +400,12 @@ AddConfigVar('warn.vm_gc_bug',
         BoolParam(False),
         in_c_key=False)
 
+AddConfigVar('warn.signal_conv2d_interface',
+             ("Warn we use the new signal.conv2d() when its interface"
+              " changed mid June 2014"),
+             BoolParam(warn_default('0.7')),
+             in_c_key=False)
+
 AddConfigVar('compute_test_value',
         ("If 'True', Theano will run each op at graph build time, using "
          "Constants, SharedVariables and the tag 'test_value' as inputs "

theano/tensor/signal/conv.py

@@ -5,6 +5,9 @@ generic 2D convolution.
 
 __docformat__ = "restructuredtext en"
 
+import warnings
+
+import theano
 import theano.tensor as tensor
 from theano.tensor.nnet import conv
 
@@ -83,6 +86,13 @@ def conv2d(input, filters, image_shape=None, filter_shape=None,
 
     # flatten to 3D tensor if convolving with single filter or single image
     if input.ndim == 2 and filters.ndim == 2:
+        if theano.config.warn.signal_conv2d_interface:
+            warnings.warn(
+                "theano.tensor.signal.conv2d() now output 2d tensor when both"
+                " inputs are 2d. To disable this warning, set the Theano flag"
+                " warn.signal_conv2d_interface to False",
+                stacklevel=3)
+
         output = tensor.flatten(output.T, outdim=2).T
     elif input.ndim == 2 or filters.ndim == 2:
         output = tensor.flatten(output.T, outdim=3).T