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MNT: when clearing an Axes via clear/cla fully detach children #24627

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Merged
merged 3 commits into from
Dec 7, 2022
Merged

MNT: when clearing an Axes via clear/cla fully detach children #24627

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MNT: when clearing an Axes via clear/cla fully detach children
tacaswell Dec 4, 2022
146b478
MNT: compress swap to one line
tacaswell Dec 5, 2022
c77fa4c
DOC: fix spelling in test
tacaswell Dec 7, 2022
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4 changes: 3 additions & 1 deletion lib/matplotlib/axes/_base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1315,7 +1315,9 @@ def __clear(self):
self._get_patches_for_fill = _process_plot_var_args(self, 'fill')

self._gridOn = mpl.rcParams['axes.grid']
self._children = []
old_children, self._children = self._children, []
for chld in old_children:
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Is there a reason for not doing for chld in getattr(self, "_children", []): ... before resetting _children?

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@tacaswell tacaswell Dec 5, 2022 •
edited
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I am more worried about the state where the Axes thinks the Artist is in the draw list rather than the case where the Artist still thinks it is in the Axes (which has been the status quo).

My first attempt was

old_children, self._children = self._children, []

but that had issues where either you check self._children before it exists or you get other attribute errors because other parts of the code are using the existence of self._children to determine if we are still in the init method or not.

I also thought about doing for chld in self._chidren: chld.remove() but was trying to avoid a lot of thrashing / maybe some premature optimization.

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not sure if compressing to one line is better or worse ....

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Perhaps a good idea to first get rid of this "not having _children" problem by pre-initing it early in __init__? e.g. something like

diff --git i/lib/matplotlib/axes/_base.py w/lib/matplotlib/axes/_base.py
index 3e665cda42..9eb65d3fc4 100644
--- i/lib/matplotlib/axes/_base.py
+++ w/lib/matplotlib/axes/_base.py
@@ -665,6 +665,8 @@ class _AxesBase(martist.Artist):
         self.set_box_aspect(box_aspect)
         self._axes_locator = None  # Optionally set via update(kwargs).
 
+        self._children = []
+
         # placeholder for any colorbars added that use this Axes.
         # (see colorbar.py):
         self._colorbars = []
@@ -1078,7 +1080,7 @@ class _AxesBase(martist.Artist):
         self.transScale.set(
             mtransforms.blended_transform_factory(
                 self.xaxis.get_transform(), self.yaxis.get_transform()))
-        for line in getattr(self, "_children", []):  # Not set during init.
+        for line in self._children:
             if not isinstance(line, mlines.Line2D):
                 continue
             try:
@@ -2936,22 +2938,15 @@ class _AxesBase(martist.Artist):
 
         x_stickies = y_stickies = np.array([])
         if self.use_sticky_edges:
-            # Only iterate over Axes and artists if needed.  The check for
-            # ``hasattr(ax, "_children")`` is necessary because this can be
-            # called very early in the Axes init process (e.g., for twin Axes)
-            # when these attributes don't even exist yet, in which case
-            # `get_children` would raise an AttributeError.
             if self._xmargin and scalex and self.get_autoscalex_on():
                 x_stickies = np.sort(np.concatenate([
                     artist.sticky_edges.x
                     for ax in self._shared_axes["x"].get_siblings(self)
-                    if hasattr(ax, "_children")
                     for artist in ax.get_children()]))
             if self._ymargin and scaley and self.get_autoscaley_on():
                 y_stickies = np.sort(np.concatenate([
                     artist.sticky_edges.y
                     for ax in self._shared_axes["y"].get_siblings(self)
-                    if hasattr(ax, "_children")
                     for artist in ax.get_children()]))
         if self.get_xscale() == 'log':
             x_stickies = x_stickies[x_stickies > 0]

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That will lead to AttributeErrors related to the Axes title attributes (and that was the point where I stopped debugging and used getattr) 🤣

I think the choice is either accept getattr or start pulling this string and see what we have to unravel which might spin out to "re-do all of the init logic in the Axes family".

chld.axes = chld.figure = None
self._mouseover_set = _OrderedSet()
self.child_axes = []
self._current_image = None # strictly for pyplot via _sci, _gci
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13 changes: 13 additions & 0 deletions lib/matplotlib/tests/test_axes.py
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Expand Up @@ -8359,6 +8359,19 @@ def test_extent_units():
im.set_extent([2, 12, date_first, date_last], clip=False)


def test_cla_clears_children_axes_and_fig():
fig, ax = plt.subplots()
lines = ax.plot([], [], [], [])
img = ax.imshow([[1]])
for art in lines + [img]:
assert art.axes is ax
assert art.figure is fig
ax.clear()
for art in lines + [img]:
assert art.axes is None
assert art.figure is None


def test_scatter_color_repr_error():

def get_next_color():
Expand Down