MNT : tweak how internals of Axes.plot work

The actual processing and artist creation in Axes.plot happens through the `__call__` method on a _process_plot_var_args instance hanging off the Axes object. The _process_plot_var_args knows what axes it is hanging off of and passed that into the Line2D artists as a kwarg at creation time, which sets the axes of the Line2D. The axes of the Line2D is set again during the `Axes.add_line` method. For the most part this is fine, if un-needed, because the axes is the same objects both time it is set. However when using the mpl_toolkit, Axes objects get wrapped in not-strictly-subclassed objects and the Axes object that the _process_plot_var_args object knows about is not the Axes object that add_line is called on which now results in an exception as it is moving artists between axes.
matplotlib · efiring · Dec 13, 2014 · Nov 23, 2014 · Nov 24, 2014 · Nov 27, 2014
commit 69decec0297f5693303297800e5e05252b4663f9
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -237,7 +237,6 @@ def _makeline(self, x, y, kw, kwargs):
            # (can't use setdefault because it always evaluates
            # its second argument)
        seg = mlines.Line2D(x, y,
-                            axes=self.axes,
                            **kw
                            )
        self.set_lineprops(seg, **kwargs)