Revert "remove example which is now redunant because of tutorial"

This reverts commit 5ad2cc8.

examples/mnist.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+
+from theano import tensor
+
+from blocks.algorithms import GradientDescent, SteepestDescent
+from blocks.bricks import MLP, Tanh, Identity
+from blocks.bricks.cost import CategoricalCrossEntropy
+from blocks.datasets import DataStream
+from blocks.datasets.mnist import MNIST
+from blocks.datasets.schemes import SequentialScheme
+from blocks.extensions import FinishAfter, Printing
+from blocks.main_loop import MainLoop
+
+
+def main():
+    mlp = MLP([Tanh(), Identity()], [784, 100, 10])
+    x = tensor.matrix('features')
+    y = tensor.lmatrix('targets')
+    cost = CategoricalCrossEntropy().apply(y.flatten() - 1, mlp.apply(x))
+
+    mnist = MNIST("train")
+
+    main_loop = MainLoop(
+        mlp,
+        DataStream(mnist,
+                   iteration_scheme=SequentialScheme(mnist.num_examples, 20)),
+        GradientDescent(cost=cost,
+                        step_rule=SteepestDescent(learning_rate=0.1)),
+        extensions=[FinishAfter(after_n_epochs=2),
+                    Printing()])
+    main_loop.run()
+
+if __name__ == "__main__":
+    main()

tests/test_examples.py

@@ -4,6 +4,7 @@
 import pylearn2
 
 import blocks
+from examples.mnist import main as mnist_test
 from examples.pylearn2.markov_chain import main as pylearn2_test
 
 
@@ -17,6 +18,12 @@ def setup():
     logger.setLevel(logging.ERROR)
 
 
+def test_mnist():
+    mnist_test()
+
+test_mnist.setup = setup
+
+
 def test_pylearn2():
     filename = 'unittest_markov_chain'
     pylearn2_test('train', filename, 0, 3, False)