Due to lack of support for the '%' as a unit within pint,

this update converts '%' units to 'percent' units within the
MetPy xarray accessor.

Fixes Unidata#1038.

metpy/tests/test_xarray.py

@@ -84,6 +84,14 @@ def test_units(test_var):
     assert test_var.metpy.units == units('kelvin')
 
 
+def test_units_percent():
+    """Test that '%' is converted to 'percent'."""
+    test_var_percent = xr.open_dataset(
+        get_test_data('irma_gfs_example.nc',
+                      as_file_obj=False))['Relative_humidity_isobaric']
+    assert test_var_percent.metpy.units == units('percent')
+
+
 def test_convert_units(test_var):
     """Test in-place conversion of units."""
     test_var.metpy.convert_units('degC')

metpy/xarray.py

@@ -34,7 +34,10 @@ def __init__(self, data_array):
 
     @property
     def units(self):
-        return units(self._units)
+        if self._units != '%':
+            return units(self._units)
+        else:
+            return units('percent')
 
     @property
     def unit_array(self):