Raise a more specific error when the date is not covered (#36)

jplephem/exceptions.py

@@ -0,0 +1,20 @@
+"""A set of special exceptions that can be thrown by the jplephem library"""
+
+class OutOfRangeTimestampError(ValueError):
+    """
+    This exception is thrown if any input times are out of the range of
+    times jplephem can compute ephemeris for.
+    It has for properties:
+
+    - `message` is a string explaining what happened,
+    - `min_timestamp` and `max_timestamp` are floats giving the minimum and
+      maximum supported times,
+    - `out_of_range_times` is an array of booleans where `True` means the
+      corresponding date in the input array is out of range and `False` means
+      it is correct.
+    """
+    def __init__(self, message, min_timestamp, max_timestamp, out_of_range_times):
+        self.message = message
+        self.min_timestamp = min_timestamp
+        self.max_timestamp = max_timestamp
+        self.out_of_range_times = out_of_range_times

jplephem/spk.py

@@ -6,6 +6,7 @@ http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/spk.html
 from numpy import array, empty, empty_like, interp, rollaxis
 from .daf import DAF
 from .descriptorlib import reify
+from .exceptions import OutOfRangeTimestampError
 from .names import target_names
 
 T0 = 2451545.0
@@ -227,8 +228,13 @@ class Segment(BaseSegment):
 
         if (index < 0).any() or (index > n).any():
             final_epoch = init + intlen * n
-            raise ValueError('segment only covers dates %.1f through %.1f'
-                            % (init, final_epoch))
+            raise OutOfRangeTimestampError(
+                'segment only covers dates %.1f through %.1f' % (init,
+                                                                 final_epoch),
+                min_timestamp=init,
+                max_timestamp=final_epoch,
+                out_of_range_times=[True if i < 0 or i > n else False
+                                    for i in index])
 
         omegas = (index == n)
         index[omegas] -= 1