Merge pull request matplotlib#22114 from anntzer/as

Rewrite AxesStack independently of cbook.Stack.

Author: greglucas

lib/matplotlib/figure.py

@@ -16,6 +16,7 @@
 
 from contextlib import ExitStack
 import inspect
+import itertools
 import logging
 from numbers import Integral
 
@@ -50,69 +51,41 @@ def _stale_figure_callback(self, val):
         self.figure.stale = val
 
 
-class _AxesStack(cbook.Stack):
+class _AxesStack:
     """
-    Specialization of Stack, to handle all tracking of Axes in a Figure.
+    Helper class to track axes in a figure.
 
-    This stack stores ``ind, axes`` pairs, where ``ind`` is a serial index
-    tracking the order in which axes were added.
-
-    AxesStack is a callable; calling it returns the current axes.
+    Axes are tracked both in the order in which they have been added
+    (``self._axes`` insertion/iteration order) and in the separate "gca" stack
+    (which is the index to which they map in the ``self._axes`` dict).
     """
 
     def __init__(self):
-        super().__init__()
-        self._ind = 0
+        self._axes = {}  # Mapping of axes to "gca" order.
+        self._counter = itertools.count()
 
     def as_list(self):
-        """
-        Return a list of the Axes instances that have been added to the figure.
-        """
-        return [a for i, a in sorted(self._elements)]
-
-    def _entry_from_axes(self, e):
-        return next(((ind, a) for ind, a in self._elements if a == e), None)
+        """List the axes that have been added to the figure."""
+        return [*self._axes]  # This relies on dict preserving order.
 
     def remove(self, a):
         """Remove the axes from the stack."""
-        super().remove(self._entry_from_axes(a))
+        self._axes.pop(a)
 
     def bubble(self, a):
-        """
-        Move the given axes, which must already exist in the stack, to the top.
-        """
-        return super().bubble(self._entry_from_axes(a))
+        """Move an axes, which must already exist in the stack, to the top."""
+        if a not in self._axes:
+            raise ValueError("Axes has not been added yet")
+        self._axes[a] = next(self._counter)
 
     def add(self, a):
-        """
-        Add Axes *a* to the stack.
-
-        If *a* is already on the stack, don't add it again.
-        """
-        # All the error checking may be unnecessary; but this method
-        # is called so seldom that the overhead is negligible.
-        _api.check_isinstance(Axes, a=a)
-
-        if a in self:
-            return
-
-        self._ind += 1
-        super().push((self._ind, a))
+        """Add an axes to the stack, ignoring it if already present."""
+        if a not in self._axes:
+            self._axes[a] = next(self._counter)
 
-    def __call__(self):
-        """
-        Return the active axes.
-
-        If no axes exists on the stack, then returns None.
-        """
-        if not len(self._elements):
-            return None
-        else:
-            index, axes = self._elements[self._pos]
-            return axes
-
-    def __contains__(self, a):
-        return a in self.as_list()
+    def current(self):
+        """Return the active axes, or None if the stack is empty."""
+        return max(self._axes, key=self._axes.__getitem__, default=None)
 
 
 class SubplotParams:
@@ -1512,10 +1485,8 @@ def gca(self, **kwargs):
                 "new axes with default keyword arguments. To create a new "
                 "axes with non-default arguments, use plt.axes() or "
                 "plt.subplot().")
-        if self._axstack.empty():
-            return self.add_subplot(1, 1, 1, **kwargs)
-        else:
-            return self._axstack()
+        ax = self._axstack.current()
+        return ax if ax is not None else self.add_subplot(**kwargs)
 
     def _gci(self):
         # Helper for `~matplotlib.pyplot.gci`.  Do not use elsewhere.
@@ -1534,13 +1505,13 @@ def _gci(self):
         Historically, the only colorable artists were images; hence the name
         ``gci`` (get current image).
         """
-        # Look first for an image in the current Axes:
-        if self._axstack.empty():
+        # Look first for an image in the current Axes.
+        ax = self._axstack.current()
+        if ax is None:
             return None
-        im = self._axstack()._gci()
+        im = ax._gci()
         if im is not None:
             return im
-
         # If there is no image in the current Axes, search for
         # one in a previously created Axes.  Whether this makes
         # sense is debatable, but it is the documented behavior.
@@ -2834,7 +2805,7 @@ def clf(self, keep_observers=False):
         toolbar = self.canvas.toolbar
         if toolbar is not None:
             toolbar.update()
-        self._axstack.clear()
+        self._axstack = _AxesStack()
         self.artists = []
         self.lines = []
         self.patches = []