For #527, try returning arrays from hstr()/dstr()

This replaces a behavior that was contributed back in, wow, 2015 — crazy
times!  Also, let’s test this behavior in unit tests for the first time.

skyfield/tests/test_units.py

@@ -2,7 +2,9 @@
 
 from assay import assert_raises
 from numpy import array
-from skyfield.units import Angle, Distance, Velocity, UnpackingError
+from skyfield.units import (
+    Angle, Distance, Velocity, UnpackingError, WrongUnitError,
+)
 
 try:
     from astropy import units as u
@@ -43,12 +45,31 @@ def test_angle_scalar_strs():
     assert str(Angle(hours=array(12))) == '''12h 00m 00.00s'''
 
 def test_angle_array_strs():
-    assert str(Angle(degrees=array([90, 91, 92]))) == (
-        '''3 values from 90deg 00' 00.0" to 92deg 00' 00.0"'''
-        )
-    assert str(Angle(hours=array([11, 12, 13]))) == (
-        '''3 values from 11h 00m 00.00s to 13h 00m 00.00s'''
-        )
+    h = Angle(hours=array([11, 12, 13]))
+    d = Angle(degrees=h._degrees)
+
+    assert str(h) == '3 values from 11h 00m 00.00s to 13h 00m 00.00s'
+    assert str(d) == '''3 values from 165deg 00' 00.0" to 195deg 00' 00.0"'''
+
+    with assert_raises(WrongUnitError):
+        h.dstr()
+        d.hstr()
+
+    assert h.hstr() == d.hstr(warn=False) == [
+        '11h 00m 00.00s',
+        '12h 00m 00.00s',
+        '13h 00m 00.00s',
+    ]
+    assert d.dstr() == h.dstr(warn=False) == [
+        '165deg 00\' 00.0"',
+        '180deg 00\' 00.0"',
+        '195deg 00\' 00.0"',
+    ]
+
+    empty = Angle(radians=[])
+    assert str(empty) == 'Angle []'
+    assert empty.hstr(warn=False) == []
+    assert empty.dstr() == []
 
 def test_angle_sexagesimal_args():
     assert str(Angle(degrees=(90,))) == '''90deg 00' 00.0"'''

skyfield/units.py

@@ -258,7 +258,17 @@ def mas(self):
     def __str__(self):
         if self.radians.size == 0:
             return 'Angle []'
-        return self.dstr() if self.preference == 'degrees' else self.hstr()
+        if self.preference == 'degrees':
+            v = self._degrees
+            f = _dstr
+        else:
+            v = self._hours
+            f = _hstr
+        shape = getattr(v, 'shape', None)
+        if shape:
+            return "{0} values from {1} to {2}".format(
+                len(v), f(v[0]), f(v[-1]))
+        return f(v)
 
     def __repr__(self):
         if self.radians.size == 0:
@@ -302,16 +312,10 @@ def hstr(self, places=2, warn=True):
         """Convert to a string like ``12h 07m 30.00s``."""
         if warn and self.preference != 'hours':
             raise WrongUnitError('hstr')
-        if self.radians.size == 0:
-            return '<Angle []>'
         hours = self._hours
         shape = getattr(hours, 'shape', ())
-        if shape and shape != (1,):
-            return "{0} values from {1} to {2}".format(
-                len(hours),
-                _hstr(hours[0], places),
-                _hstr(hours[-1], places),
-                )
+        if shape:
+            return [_hstr(h, places) for h in hours]
         return _hstr(hours, places)
 
     def dms(self, warn=True):
@@ -340,17 +344,11 @@ def dstr(self, places=1, warn=True):
         """Convert to a string like ``181deg 52\' 30.0"``."""
         if warn and self.preference != 'degrees':
             raise WrongUnitError('dstr')
-        if self.radians.size == 0:
-            return '<Angle []>'
         degrees = self._degrees
         signed = self.signed
         shape = getattr(degrees, 'shape', ())
-        if shape and shape != (1,):
-            return "{0} values from {1} to {2}".format(
-                len(degrees),
-                _dstr(degrees[0], places, signed),
-                _dstr(degrees[-1], places, signed),
-                )
+        if shape:
+            return [_dstr(d, places, signed) for d in degrees]
         return _dstr(degrees, places, signed)
 
     def to(self, unit):