MNT: re-arrange where check is done

jklymak · jklymak · commit c1fe98d62a96 · 2022-12-12T15:09:51.000-08:00
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -1087,6 +1087,16 @@ def legend(self, *args, **kwargs):
         ----------------
         %(_legend_kw_doc)s
 
+        If a figure is using the constrained layout manager, the string codes
+        of the *loc* keyword argument can get better layout behaviour using the
+        prefix 'outside'. There is ambiguity at the corners, so 'outside
+        upper right' will make space for the legend above the rest of the
+        axes in the layout, and 'outside right upper' will make space on the
+        right side of the layout.  In addition to the values of *loc*
+        listed above, we have 'outside right upper', 'outside right lower',
+        'outside left upper', and 'outside left lower'.  See
+        :doc:`/tutorials/intermediate/legend_guide` for more details.
+
         See Also
         --------
         .Axes.legend
@@ -1113,32 +1123,9 @@ def legend(self, *args, **kwargs):
             # extra_args = extra_args[1:]
             pass
         transform = kwargs.pop('bbox_transform', self.transSubfigure)
-        outside = None
-        if 'loc' in kwargs:
-            # need to protect this in case loc was passed in
-            # positionally...
-            loc = kwargs.pop('loc', None)
-            # handle outside legends:
-            if isinstance(loc, str):
-                if loc.split()[0] == 'outside':
-                    # strip outside:
-                    loc = loc.split('outside ')[1]
-                    # strip "center" at the beginning
-                    outside = loc.replace('center ', '')
-                    # strip first
-                    outside = outside.split()[0]
-                    locs = loc.split()
-                    if len(locs) > 1 and locs[0] in ('right', 'left'):
-                        # locs doesn't accept "left upper", etc, so swap
-                        if locs[0] != 'center':
-                            locs = locs[::-1]
-                        loc = locs[0] + ' ' + locs[1]
-
-            kwargs['loc'] = loc
         # explicitly set the bbox transform if the user hasn't.
         l = mlegend.Legend(self, handles, labels, *extra_args,
                            bbox_transform=transform, **kwargs)
-        l._outside = outside
         self.legends.append(l)
         l._remove_method = self.legends.remove
         self.stale = True
diff --git a/lib/matplotlib/legend.py b/lib/matplotlib/legend.py
@@ -465,13 +465,39 @@ def val_or_rc(val, rc_name):
             )
         self.parent = parent
 
+        loc0 = loc
         self._loc_used_default = loc is None
         if loc is None:
             loc = mpl.rcParams["legend.loc"]
             if not self.isaxes and loc in [0, 'best']:
                 loc = 'upper right'
+
+        # handle outside legends:
+        self._outside = None
         if isinstance(loc, str):
+            if loc.split()[0] == 'outside':
+                # strip outside:
+                loc = loc.split('outside ')[1]
+                # strip "center" at the beginning
+                self._outside = loc.replace('center ', '')
+                # strip first
+                self._outside = self._outside.split()[0]
+                locs = loc.split()
+                if len(locs) > 1 and locs[0] in ('right', 'left'):
+                    # locs doesn't accept "left upper", etc, so swap
+                    if locs[0] != 'center':
+                        locs = locs[::-1]
+                    loc = locs[0] + ' ' + locs[1]
+            # check that loc is in acceptable strings
             loc = _api.check_getitem(self.codes, loc=loc)
+
+        if self.isaxes and self._outside:
+            # warn if user has done "outside upper right", but don't
+            # error because at this point we just drop the "outside".
+            raise UserWarning(
+                f"'outside' option for loc='{loc0}' keyword argument only "
+                "works for figure legends")
+
         if not self.isaxes and loc == 0:
             raise ValueError(
                 "Automatic legend placement (loc='best') not implemented for "
