PythonLayer takes parameters by string

include/caffe/python_layer.hpp

@@ -18,6 +18,8 @@ class PythonLayer : public Layer<Dtype> {
 
   virtual void LayerSetUp(const vector<Blob<Dtype>*>& bottom,
       const vector<Blob<Dtype>*>& top) {
+    self_.attr("param_str") = bp::str(
+        this->layer_param_.python_param().param_str());
     self_.attr("setup")(bottom, top);
   }
   virtual void Reshape(const vector<Blob<Dtype>*>& bottom,

python/caffe/test/test_python_layer_with_param_str.py

@@ -0,0 +1,59 @@
+import unittest
+import tempfile
+import os
+import six
+
+import caffe
+
+
+class SimpleParamLayer(caffe.Layer):
+    """A layer that just multiplies by the numeric value of its param string"""
+
+    def setup(self, bottom, top):
+        try:
+            self.value = float(self.param_str)
+        except ValueError:
+            raise ValueError("Parameter string must be a legible float")
+
+    def reshape(self, bottom, top):
+        top[0].reshape(*bottom[0].data.shape)
+
+    def forward(self, bottom, top):
+        top[0].data[...] = self.value * bottom[0].data
+
+    def backward(self, top, propagate_down, bottom):
+        bottom[0].diff[...] = self.value * top[0].diff
+
+
+def python_param_net_file():
+    with tempfile.NamedTemporaryFile(mode='w+', delete=False) as f:
+        f.write("""name: 'pythonnet' force_backward: true
+        input: 'data' input_shape { dim: 10 dim: 9 dim: 8 }
+        layer { type: 'Python' name: 'mul10' bottom: 'data' top: 'mul10'
+          python_param { module: 'test_python_layer_with_param_str'
+                layer: 'SimpleParamLayer' param_str: '10' } }
+        layer { type: 'Python' name: 'mul2' bottom: 'mul10' top: 'mul2'
+          python_param { module: 'test_python_layer_with_param_str'
+                layer: 'SimpleParamLayer' param_str: '2' } }""")
+        return f.name
+
+
+class TestLayerWithParam(unittest.TestCase):
+    def setUp(self):
+        net_file = python_param_net_file()
+        self.net = caffe.Net(net_file, caffe.TRAIN)
+        os.remove(net_file)
+
+    def test_forward(self):
+        x = 8
+        self.net.blobs['data'].data[...] = x
+        self.net.forward()
+        for y in self.net.blobs['mul2'].data.flat:
+            self.assertEqual(y, 2 * 10 * x)
+
+    def test_backward(self):
+        x = 7
+        self.net.blobs['mul2'].diff[...] = x
+        self.net.backward()
+        for y in self.net.blobs['data'].diff.flat:
+            self.assertEqual(y, 2 * 10 * x)

src/caffe/proto/caffe.proto

@@ -703,6 +703,11 @@ message PowerParameter {
 message PythonParameter {
   optional string module = 1;
   optional string layer = 2;
+  // This value is set to the attribute `param_str` of the `PythonLayer` object
+  // in Python before calling the `setup()` method. This could be a number,
+  // string, dictionary in Python dict format, JSON, etc. You may parse this
+  // string in `setup` method and use it in `forward` and `backward`.
+  optional string param_str = 3 [default = ''];
 }
 
 // Message that stores parameters used by ReductionLayer