Fixed formatter in IntervalQueryParam

pyvo/dal/params.py

@@ -380,7 +380,7 @@ def __init__(self, unit=None, equivalencies=None):
         super().__init__()
 
     def get_dal_format(self, val):
-        if isinstance(val, tuple):
+        if isinstance(val, (tuple, Quantity)):
             if len(val) == 1:
                 high = low = val[0]
             elif len(val) == 2:
@@ -391,16 +391,21 @@ def get_dal_format(self, val):
                                  format(val))
         else:
             high = low = val
+        if isinstance(low, (int, float)) and isinstance(high, (int, float))\
+                and low > high:
+            raise ValueError('Invalid interval: min({}) > max({})'.format(
+                low, high))
         if self._unit:
             if not isinstance(low, Quantity):
                 low = low*self._unit
             low = low.to(self._unit, equivalencies=self._equivalencies).value
             if not isinstance(high, Quantity):
                 high = high*self._unit
             high = high.to(self._unit, equivalencies=self._equivalencies).value
-        if low > high:
-            raise ValueError('Invalid interval: min({}) > max({})'.format(
-                low, high))
+
+            if low > high:
+                # interval could become invalid during transform (e.g. GHz->m)
+                low, high = high, low
 
         return '{} {}'.format(low, high)
 

pyvo/dal/tests/test_params.py

@@ -8,7 +8,7 @@
 
 from pyvo.dal.adhoc import DatalinkResults
 from pyvo.dal.params import find_param_by_keyword, get_converter,\
-    AbstractDalQueryParam
+    AbstractDalQueryParam, IntervalQueryParam
 from pyvo.dal.exceptions import DALServiceError
 
 import pytest
@@ -207,3 +207,18 @@ def get_dal_format(self, item):
     test_obs.clear()
     assert len(test_obs) == 0
     assert len(test_obs.dal) == 0
+
+
+def test_dal_format():
+    iqp = IntervalQueryParam(unit=u.m, equivalencies=u.spectral())
+    assert '1.0 1.0' == iqp.get_dal_format(1)
+    assert '1.0 2.0' == iqp.get_dal_format((1, 2))
+    assert '1.0 2.0' == iqp.get_dal_format((100*u.cm, 200*u.cm))
+    assert '1.0 2.0' == iqp.get_dal_format((100, 200)*u.cm)
+    assert '0.14989622900000002 1.0' == iqp.get_dal_format((100*u.cm, 2*u.GHz))
+    assert '14.9896229 29.9792458' == iqp.get_dal_format((0.01, 0.02)*u.GHz)
+    # Quantity intervals are corrected in terms of min and max ..
+    assert '1.0 2.0' == iqp.get_dal_format((2, 1)*u.m)
+    # But unitless intervals are not
+    with pytest.raises(ValueError):
+        iqp.get_dal_format((2, 1))