Add docstrings.

level1c4pps/calibration_coefs.py

@@ -82,6 +82,14 @@ def get_calibration(platform, time, clip=False):
 
 
 def _get_single_channel_calibration(platform, channel, time, clip):
+    """Get calibration coefficients for a single channel.
+
+    Args:
+        platform: Platform name.
+        channel: Channel name.
+        time: Observation date or time.
+        clip: Clip at time coverage boundaries of the calibration dataset.
+    """
     time = _prepare_time(time, clip)
     gain, offset = calib_meirink(platform, channel, time)
     return {'gain': gain, 'offset': offset}

level1c4pps/tests/test_seviri2pps.py

@@ -621,6 +621,7 @@ def test_clip_at_time_coverage_bounds(self, coverage_boundary, outside_coverage)
         self._assert_coefs_close(coefs1, coefs2)
 
     def test_fails_with_invalid_time(self):
+        """Test that calibration fails with timestamps < reference time."""
         with pytest.raises(ValueError):
             calib.get_calibration(
                 platform='MSG1',