matplotlib · jklymak · Feb 2, 2019 · Jan 23, 2019 · timhoffm · Jan 28, 2019
diff --git a/doc/api/next_api_changes/2018-01-22-AL.rst b/doc/api/next_api_changes/2018-01-22-AL.rst
@@ -0,0 +1,4 @@
+Deprecations
+````````````
+
+``projections.process_projection_requirements`` is deprecated.
diff --git a/lib/matplotlib/axes/_subplots.py b/lib/matplotlib/axes/_subplots.py
@@ -1,4 +1,5 @@
 import functools
+import uuid
 
 from matplotlib import docstring
 import matplotlib.artist as martist
@@ -157,33 +158,33 @@ def label_outer(self):
             self.get_yaxis().get_offset_text().set_visible(False)
             self.set_ylabel("")
 
-    def _make_twin_axes(self, *kl, **kwargs):
+    def _make_twin_axes(self, *args, **kwargs):
         """
         Make a twinx axes of self. This is used for twinx and twiny.
         """
-        from matplotlib.projections import process_projection_requirements
         if 'sharex' in kwargs and 'sharey' in kwargs:
             # The following line is added in v2.2 to avoid breaking Seaborn,
             # which currently uses this internal API.
             if kwargs["sharex"] is not self and kwargs["sharey"] is not self:
-                raise ValueError("Twinned Axes may share only one axis.")
-        kl = (self.get_subplotspec(),) + kl
-        projection_class, kwargs, key = process_projection_requirements(
-            self.figure, *kl, **kwargs)
-
-        ax2 = subplot_class_factory(projection_class)(self.figure,
-                                                      *kl, **kwargs)
-        self.figure.add_subplot(ax2)
+                raise ValueError("Twinned Axes may share only one axis")
+        # The dance here with label is to force add_subplot() to create a new
+        # Axes (by passing in a label never seen before).  Note that this does
+        # not affect plot reactivation by subplot() as twin axes can never be
+        # reactivated by subplot().
+        sentinel = str(uuid.uuid4())
+        real_label = kwargs.pop("label", sentinel)
+        twin = self.figure.add_subplot(
+            self.get_subplotspec(), *args, label=sentinel, **kwargs)
+        if real_label is not sentinel:
+            twin.set_label(real_label)
         self.set_adjustable('datalim')
-        ax2.set_adjustable('datalim')
-
-        if self._layoutbox is not None and ax2._layoutbox is not None:
+        twin.set_adjustable('datalim')
+        if self._layoutbox is not None and twin._layoutbox is not None:
             # make the layout boxes be explicitly the same
-            ax2._layoutbox.constrain_same(self._layoutbox)
-            ax2._poslayoutbox.constrain_same(self._poslayoutbox)
-
-        self._twinned_axes.join(self, ax2)
-        return ax2
+            twin._layoutbox.constrain_same(self._layoutbox)
+            twin._poslayoutbox.constrain_same(self._poslayoutbox)
+        self._twinned_axes.join(self, twin)
+        return twin
 
 
 # this here to support cartopy which was using a private part of the

diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -17,7 +17,7 @@
 import numpy as np
 
 from matplotlib import rcParams
-from matplotlib import backends, docstring
+from matplotlib import backends, docstring, projections
 from matplotlib import __version__ as _mpl_version
 from matplotlib import get_backend
 
@@ -1021,6 +1021,42 @@ def delaxes(self, ax):
             func(self)
         self.stale = True
 
+    def add_artist(self, artist, clip=False):
+        """
+        Add any :class:`~matplotlib.artist.Artist` to the figure.
+
+        Usually artists are added to axes objects using
+        :meth:`matplotlib.axes.Axes.add_artist`, but use this method in the
+        rare cases that adding directly to the figure is necessary.
+
+        Parameters
+        ----------
+        artist : `~matplotlib.artist.Artist`
+            The artist to add to the figure. If the added artist has no
+            transform previously set, its transform will be set to
+            ``figure.transFigure``.
+        clip : bool, optional, default ``False``
+            An optional parameter ``clip`` determines whether the added artist
+            should be clipped by the figure patch. Default is *False*,
+            i.e. no clipping.
+
+        Returns
+        -------
+        artist : The added `~matplotlib.artist.Artist`
+        """
+        artist.set_figure(self)
+        self.artists.append(artist)
+        artist._remove_method = self.artists.remove
+
+        if not artist.is_transform_set():
+            artist.set_transform(self.transFigure)
+
+        if clip:
+            artist.set_clip_path(self.patch)
+
+        self.stale = True
+        return artist
+
     def _make_key(self, *args, **kwargs):
         """Make a hashable key out of args and kwargs."""
 
@@ -1051,41 +1087,37 @@ def fixlist(args):
         key = fixlist(args), fixitems(kwargs.items())
         return key
 
-    def add_artist(self, artist, clip=False):
+    def _process_projection_requirements(
+            self, *args, polar=False, projection=None, **kwargs):
         """
-        Add any :class:`~matplotlib.artist.Artist` to the figure.
+        Handle the args/kwargs to add_axes/add_subplot/gca, returning::
 
-        Usually artists are added to axes objects using
-        :meth:`matplotlib.axes.Axes.add_artist`, but use this method in the
-        rare cases that adding directly to the figure is necessary.
+            (axes_proj_class, proj_class_kwargs, proj_stack_key)
 
-        Parameters
-        ----------
-        artist : `~matplotlib.artist.Artist`
-            The artist to add to the figure. If the added artist has no
E30A            transform previously set, its transform will be set to
-            ``figure.transFigure``.
-        clip : bool, optional, default ``False``
-            An optional parameter ``clip`` determines whether the added artist
-            should be clipped by the figure patch. Default is *False*,
-            i.e. no clipping.
-
-        Returns
-        -------
-        artist : The added `~matplotlib.artist.Artist`
+        which can be used for new axes initialization/identification.
         """
-        artist.set_figure(self)
-        self.artists.append(artist)
-        artist._remove_method = self.artists.remove
-
-        if not artist.is_transform_set():
-            artist.set_transform(self.transFigure)
+        if polar:
+            if projection is not None and projection != 'polar':
+                raise ValueError(
+                    "polar=True, yet projection=%r. "
+                    "Only one of these arguments should be supplied." %
+                    projection)
+            projection = 'polar'
+
+        if isinstance(projection, str) or projection is None:
+            projection_class = projections.get_projection_class(projection)
+        elif hasattr(projection, '_as_mpl_axes'):
+            projection_class, extra_kwargs = projection._as_mpl_axes()
+            kwargs.update(**extra_kwargs)
+        else:
+            raise TypeError('projection must be a string, None or implement a '
+                            '_as_mpl_axes method. Got %r' % projection)
 
-        if clip:
-            artist.set_clip_path(self.patch)
+        # Make the key without projection kwargs, this is used as a unique
+        # lookup for axes instances
+        key = self._make_key(*args, **kwargs)
 
-        self.stale = True
-        return artist
+        return projection_class, kwargs, key
 
     @docstring.dedent_interpd
     def add_axes(self, *args, **kwargs):
@@ -1199,8 +1231,8 @@ def add_axes(self, *args, **kwargs):
             if not np.isfinite(rect).all():
                 raise ValueError('all entries in rect must be finite '
                                  'not {}'.format(rect))
-            projection_class, kwargs, key = process_projection_requirements(
-                self, *args, **kwargs)
+            projection_class, kwargs, key = \
+                self._process_projection_requirements(*args, **kwargs)
 
             # check that an axes of this type doesn't already exist, if it
             # does, set it as active and return it
@@ -1212,12 +1244,7 @@ def add_axes(self, *args, **kwargs):
             # create the new axes using the axes class given
             a = projection_class(self, rect, **kwargs)
 
-        self._axstack.add(key, a)
-        self.sca(a)
-        a._remove_method = self._remove_ax
-        self.stale = True
-        a.stale_callback = _stale_figure_callback
-        return a
+        return self._add_axes_internal(key, a)
 
     @docstring.dedent_interpd
     def add_subplot(self, *args, **kwargs):
@@ -1351,8 +1378,8 @@ def add_subplot(self, *args, **kwargs):
             # in the hash)
             key = self._make_key(*args, **kwargs)
         else:
-            projection_class, kwargs, key = process_projection_requirements(
-                self, *args, **kwargs)
+            projection_class, kwargs, key = \
+                self._process_projection_requirements(*args, **kwargs)
 
             # try to find the axes with this key in the stack
             ax = self._axstack.get(key)
@@ -1371,12 +1398,17 @@ def add_subplot(self, *args, **kwargs):
                     self._axstack.remove(ax)
 
             a = subplot_class_factory(projection_class)(self, *args, **kwargs)
-        self._axstack.add(key, a)
-        self.sca(a)
-        a._remove_method = self._remove_ax
+
+        return self._add_axes_internal(key, a)
+
+    def _add_axes_internal(self, key, ax):
+        """Private helper for `add_axes` and `add_subplot`."""
+        self._axstack.add(key, ax)
+        self.sca(ax)
+        ax._remove_method = self._remove_ax
         self.stale = True
-        a.stale_callback = _stale_figure_callback
-        return a
+        ax.stale_callback = _stale_figure_callback
+        return ax
 
     def subplots(self, nrows=1, ncols=1, sharex=False, sharey=False,
                  squeeze=True, subplot_kw=None, gridspec_kw=None):
@@ -1868,8 +1900,8 @@ def gca(self, **kwargs):
             # if the user has specified particular projection detail
             # then build up a key which can represent this
             else:
-                projection_class, _, key = process_projection_requirements(
-                    self, **kwargs)
+                projection_class, _, key = \
+                    self._process_projection_requirements(**kwargs)
 
                 # let the returned axes have any gridspec by removing it from
                 # the key

diff --git a/lib/matplotlib/projections/__init__.py b/lib/matplotlib/projections/__init__.py
@@ -1,4 +1,4 @@
-from .. import axes
+from .. import axes, cbook
 from .geo import AitoffAxes, HammerAxes, LambertAxes, MollweideAxes
 from .polar import PolarAxes
 
@@ -60,37 +60,9 @@ def get_projection_class(projection=None):
         raise ValueError("Unknown projection %r" % projection)
 
 
-def process_projection_requirements(
-        figure, *args, polar=False, projection=None, **kwargs):
-    """
-    Handle the args/kwargs to add_axes/add_subplot/gca, returning::
-
-        (axes_proj_class, proj_class_kwargs, proj_stack_key)
-
-    which can be used for new axes initialization/identification.
-    """
-    if polar:
-        if projection is not None and projection != 'polar':
-            raise ValueError(
-                "polar=True, yet projection=%r. "
-                "Only one of these arguments should be supplied." %
-                projection)
-        projection = 'polar'
-
-    if isinstance(projection, str) or projection is None:
-        projection_class = get_projection_class(projection)
-    elif hasattr(projection, '_as_mpl_axes'):
-        projection_class, extra_kwargs = projection._as_mpl_axes()
-        kwargs.update(**extra_kwargs)
-    else:
-        raise TypeError('projection must be a string, None or implement a '
-                        '_as_mpl_axes method. Got %r' % projection)
-
-    # Make the key without projection kwargs, this is used as a unique
-    # lookup for axes instances
-    key = figure._make_key(*args, **kwargs)
-
-    return projection_class, kwargs, key
+@cbook.deprecated("3.1")
+def process_projection_requirements(figure, *args, **kwargs):
+    return figure._process_projection_requirements(*args, **kwargs)
 
 
 def get_projection_names():