Improve nonuniform timestamps error message for prilliman and detect_clearsky (#1490)

* edit error message for unequal times

* similar edits to prilliman docstring

* whatsnew

Author: kandersolar

docs/sphinx/source/whatsnew/v0.9.2.rst

@@ -14,6 +14,9 @@ Enhancements
 * Add :py:func:`pvlib.tracking.calc_surface_orientation` for calculating
   single-axis tracker ``surface_tilt`` and ``surface_azimuth`` from
   rotation angles. (:issue:`1471`, :pull:`1480`)
+* Improve error message about uneven time intervals for
+  :py:func:`~pvlib.clearsky.detect_clearsky` and :py:func:`~pvlib.temperature.prilliman`
+  (:issue:`1476`, :pull:`1490`)
 
 Bug fixes
 ~~~~~~~~~
@@ -59,3 +62,4 @@ Contributors
 * Cliff Hansen (:ghuser:`cwhanse`)
 * Jules Chéron (:ghuser:`jules-ch`)
 * Kurt Rhee (:ghuser:`kurt-rhee`)
+* Will Hobbs (:ghuser:`williamhobbs`)

pvlib/temperature.py

@@ -839,7 +839,8 @@ def prilliman(temp_cell, wind_speed, unit_mass=11.1, coefficients=None):
     .. warning::
         This implementation requires the time series inputs to be regularly
         sampled in time with frequency less than 20 minutes.  Data with
-        irregular time steps should be resampled prior to using this function.
+        irregular time steps (including from data gaps, missing leap days,
+        etc) should be resampled prior to using this function.
 
     Parameters
     ----------

pvlib/tools.py

@@ -406,5 +406,9 @@ def _get_sample_intervals(times, win_length):
         samples_per_window = int(win_length / sample_interval)
         return sample_interval, samples_per_window
     else:
-        raise NotImplementedError('algorithm does not yet support unequal '
-                                  'times. consider resampling your data.')
+        message = (
+            'algorithm does not yet support unequal time intervals. consider '
+            'resampling your data and checking for gaps from missing '
+            'periods, leap days, etc.'
+        )
+        raise NotImplementedError(message)