def set_optional_property(destination, source, prop_name):
    ' Copies the property value if present. '
    if (prop_name in source):
        destination[prop_name] = source[prop_name]
Copies the property value if present.
def set_optional_property(destination, source, prop_name):
    '  '
    if (prop_name in source):
        destination[prop_name] = source[prop_name]