Merge pull request #971 from swapsha96/fix/911

Update 'tstart' in 'shift' method if present and unit test

Author: matteobachetti

docs/changes/971.bugfix.rst

@@ -0,0 +1 @@
+The ``shift()`` method on ``Lightcurve`` and other ``StingrayTimeseries`` objects updates the ``tstart`` attribute correctly.

docs/contributing.rst

@@ -418,5 +418,5 @@ Attribution
 ~~~~~~~~~~~
 
 This Code of Conduct is adapted from the `Contributor
-Covenant <http://contributor-covenant.org>`__, version 1.4, available at
-`http://contributor-covenant.org/version/1/4 <http://contributor-covenant.org/version/1/4/>`__
+Covenant <https://contributor-covenant.org>`__, version 1.4, available at
+`https://contributor-covenant.org/version/1/4 <https://contributor-covenant.org/version/1/4/>`__

stingray/base.py

@@ -1554,7 +1554,7 @@ def change_mjdref(self, new_mjdref: float, inplace=False) -> StingrayTimeseries:
         return ts
 
     def shift(self, time_shift: float, inplace=False) -> StingrayTimeseries:
-        """Shift the time and the GTIs by the same amount
+        """Shift the time, GTIs and tstart by the same amount
 
         Parameters
         ----------
@@ -1583,6 +1583,9 @@ def shift(self, time_shift: float, inplace=False) -> StingrayTimeseries:
         if ts._gti is not None:
             ts._gti = np.asanyarray(ts._gti) + time_shift  # type: ignore
 
+        if hasattr(ts, "tstart") and ts.tstart is not None:
+            ts.tstart += time_shift
+
         return ts
 
     def _operation_with_other_obj(

stingray/tests/test_lightcurve.py

@@ -1379,8 +1379,10 @@ def test_shift(self):
         lc = Lightcurve(times, counts, input_counts=True)
         lc2 = lc.shift(1)
         assert np.allclose(lc2.time - 1, times)
+        assert lc2.tstart == lc.tstart + 1
         lc2 = lc.shift(-1)
         assert np.allclose(lc2.time + 1, times)
+        assert lc2.tstart == lc.tstart - 1
         assert np.allclose(lc2.counts, lc.counts)
         assert np.allclose(lc2.countrate, lc.countrate)
         lc = Lightcurve(times, counts, input_counts=False)