Fixed a bug with transform_with_sun_center that assumed that the glob…

…al variable would be False
sunpy · Apr 13, 2020 · 7a64843 · 7a64843
1 parent 3b4fad6
commit 7a64843
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diff --git a/changelog/4015.bugfix.rst b/changelog/4015.bugfix.rst
@@ -0,0 +1,2 @@
+Fixed a bug with :func:`~sunpy.coordinates.transformations.transform_with_sun_center` where the global variable was sometimes restored incorrectly.
+This bug was most likely encountered if there was a nested use of this context manager.
diff --git a/sunpy/coordinates/tests/test_transformations.py b/sunpy/coordinates/tests/test_transformations.py
@@ -782,7 +782,7 @@ def test_transform_with_sun_center():
 
 
 def test_transform_with_sun_center_reset():
-    # This test sequence ensures that the context manager does not change anything permanently
+    # This test sequence ensures that the context manager resets propoerly
 
     sun_center = SkyCoord(0*u.deg, 0*u.deg, 0*u.AU,
                           frame=HeliographicStonyhurst(obstime="2001-01-01"))
@@ -801,6 +801,15 @@ def test_transform_with_sun_center_reset():
     assert_quantity_allclose(result2.lat, sun_center.lat)
     assert_quantity_allclose(result2.distance, sun_center.radius)
 
+    # Exiting a nested context manager should not affect the outer context manager
+    with transform_with_sun_center():
+        with transform_with_sun_center():
+            pass
+        result2a = sun_center.transform_to(end_frame)
+    assert_quantity_allclose(result2a.lon, result2.lon)
+    assert_quantity_allclose(result2a.lat, result2.lat)
+    assert_quantity_allclose(result2a.distance, result2.distance)
+
     # After the context manager, the coordinate should have the same result as the first transform
     result3 = sun_center.transform_to(end_frame)
     assert_quantity_allclose(result3.lon, result1.lon)

diff --git a/sunpy/coordinates/transformations.py b/sunpy/coordinates/transformations.py
@@ -114,11 +114,13 @@ def transform_with_sun_center():
     try:
         global _ignore_sun_motion
 
+        old_ignore_sun_motion = _ignore_sun_motion  # nominally False
+
         log.debug("Ignore the motion of the center of the Sun for transformations")
         _ignore_sun_motion = True
         yield
     finally:
-        _ignore_sun_motion = False
+        _ignore_sun_motion = old_ignore_sun_motion
 
 
 # Global counter to keep track of the layer of transformation