Provide support for yaml constructors !degrees and !radians

src/xacro/__init__.py

@@ -101,9 +101,30 @@ def __getattr__(self, item):
 
     __getitem__ = __getattr__
 
+
+def construct_angle_radians(loader, node):
+    """utility function to construct radian values from yaml"""
+    value = loader.construct_scalar(node).strip()
+    try:
+        return float(eval(value, global_symbols, global_symbols))
+    except SyntaxError as e:
+        raise XacroException("invalid expression: %s" % value)
+
+
+def construct_angle_degrees(loader, node):
+    """utility function for converting degrees into radians from yaml"""
+    value = loader.construct_scalar(node)
+    try:
+        return math.radians(float(value))
+    except ValueError:
+        raise XacroException("invalid degree value: %s" % value)
+
+
 def load_yaml(filename):
     try:
         import yaml
+        yaml.SafeLoader.add_constructor(u'!radians', construct_angle_radians)
+        yaml.SafeLoader.add_constructor(u'!degrees', construct_angle_degrees)
     except:
         raise XacroException("yaml support not available; install python-yaml")
 

test/constructors.yaml

@@ -0,0 +1,3 @@
+a: !degrees 180
+b: !radians 0.5*pi
+c: 42

test/test_xacro.py

@@ -14,6 +14,7 @@
 import subprocess
 import re
 import ast
+import math
 try:
     from cStringIO import StringIO # Python 2.x
 except ImportError:
@@ -1173,6 +1174,15 @@ def test_yaml_support_key_in_dict(self):
         res = '''<a>True False</a>'''
         self.assert_matches(self.quick_xacro(src), res)
 
+    def test_yaml_custom_constructors(self):
+        src = '''
+<a xmlns:xacro="http://www.ros.org/wiki/xacro">
+  <xacro:property name="values" value="${load_yaml('constructors.yaml')}"/>
+  <values a="${values.a}" b="${values.b}" c="${values.c}"/>
+</a>'''
+        res = '''<a><values a="{}" b="{}" c="42"/></a>'''.format(math.pi, 0.5*math.pi)
+        self.assert_matches(self.quick_xacro(src), res)
+
     def test_macro_default_param_evaluation_order(self):
         src='''<a xmlns:xacro="http://www.ros.org/wiki/xacro">
 <xacro:macro name="foo" params="arg:=${2*foo}">