[ATTR/SYMBOL] Expose op_name attr to python (#132)

* [ATTR/SYMBOL] Expose op_name attr to python

* fix xcode

nnvm/src/core/symbolic.cc

@@ -473,6 +473,9 @@ bool Symbol::GetAttr(const std::string& key, std::string* out) const {
   if (key == "name") {
     *out = node->attrs.name;
     return true;
+  } else if (key == "op_name") {
+    *out = node->attrs.op->name;
+    return true;
   }
   auto it = node->attrs.dict.find(key);
   if (it == node->attrs.dict.end()) return false;

nnvm/tests/python/test_symbol.py

@@ -45,6 +45,15 @@ def test_copy():
                 name='exp', gpu=1, attr={"kk": "1"})
     assert y.__copy__().debug_str() == y.debug_str()
 
+
+def test_op_name():
+    x = sym.Variable('x')
+    y = sym.exp(x)
+    op_name = y.attr("op_name")
+    op_func = sym.__dict__[op_name]
+    z = op_func(x)
+
+
 def test_control_dep():
     x = sym.Variable('x')
     y = sym.conv2d(data=x, name='conv')
@@ -53,6 +62,7 @@ def test_control_dep():
     t._add_control_deps([z, y])
 
 if __name__ == "__main__":
+    test_op_name()
     test_copy()
     test_default_input()
     test_compose()