Make it possible to str() a vector Distance

brandon-rhodes · brandon-rhodes · commit 62cca330414c · 2015-02-08T12:48:28.000-05:00
Without this tweak, the attempt to print was dying with an error, because a NumPy array does not know what to do with a '.6' format string: Traceback (most recent call last): File "tmp9.py", line 9, in <module> print(mars(tt=2457061.5).position) File "/home/brandon/skyfield/skyfield/units.py", line 50, in __str__ return '{0:.6} AU'.format(self.AU) TypeError: non-empty format string passed to object.__format__ In response I have opened: numpy/numpy#5543
diff --git a/skyfield/tests/test_units.py b/skyfield/tests/test_units.py
@@ -1,6 +1,7 @@
 """Tests of whether units behave."""
 
 from assay import assert_raises
+from numpy import array
 from skyfield import units
 
 try:
@@ -10,6 +11,10 @@
 
 # needs_astropy = pytest.mark.skipif(u is None, reason='cannot import AstroPy')
 
+def test_stringifying_vector_distance():
+    a = array([1.23, 4.56])
+    assert str(units.Distance(AU=a)) == '[ 1.23  4.56] AU'
+
 def test_iterating_over_raw_measurement():
     distance = units.Distance(AU=1.234)
     with assert_raises(units.UnpackingError):
diff --git a/skyfield/units.py b/skyfield/units.py
@@ -34,6 +34,8 @@ def __init__(self, AU=None, km=None, m=None):
         elif m is not None:
             self.m = _auto_convert(m)
             self.AU = m / AU_M
+        else:
+            raise ValueError('to construct a Distance provide AU, km, or m')
 
     def __getattr__(self, name):
         if name == 'km':
@@ -45,7 +47,8 @@ def __getattr__(self, name):
         raise AttributeError('no attribute named %r' % (name,))
 
     def __str__(self):
-        return '{0:.6} AU'.format(self.AU)
+        AU = self.AU
+        return ('{0} AU' if hasattr(AU, 'shape') else '{0:.6} AU').format(AU)
 
     def __repr__(self):
         return '<{0} {1}>'.format(type(self).__name__, self)
