Pandas Series not supported as data kwarg

[stilley2]

Bug report

Bug summary

Passing a pandas Series object to axes.plot as data doesn't work.

This used to work in matplotlib 2.

Code for reproduction

from matplotlib import figure
from matplotlib.backends.backend_agg import FigureCanvasAgg
import pandas as pd


if __name__ == '__main__':
    fig = figure.Figure()
    ax = fig.add_subplot(1, 1, 1)
    data = pd.Series(data=[0, 1], index=['xdata', 'ydata'])
    print(data['xdata'])
    print(data['ydata'])
    ax.plot('xdata', 'ydata', data=data, marker='o')
    canvas = FigureCanvasAgg(fig)
    canvas.print_figure('test.png')

Actual outcome

0
1
Traceback (most recent call last):
  File "test1.py", line 12, in <module>
    ax.plot('xdata', 'ydata', data=data, marker='o')
  File "/home/stilley2/anaconda3/envs/testmpl/lib/python3.7/site-packages/matplotlib/__init__.py", line 1805, in inner
    return func(ax, *args, **kwargs)
  File "/home/stilley2/anaconda3/envs/testmpl/lib/python3.7/site-packages/matplotlib/axes/_axes.py", line 1603, in plot
    for line in self._get_lines(*args, **kwargs):
  File "/home/stilley2/anaconda3/envs/testmpl/lib/python3.7/site-packages/matplotlib/axes/_base.py", line 393, in _grab_next_args
    yield from self._plot_args(this, kwargs)
  File "/home/stilley2/anaconda3/envs/testmpl/lib/python3.7/site-packages/matplotlib/axes/_base.py", line 342, in _plot_args
    linestyle, marker, color = _process_plot_format(tup[-1])
  File "/home/stilley2/anaconda3/envs/testmpl/lib/python3.7/site-packages/matplotlib/axes/_base.py", line 118, in _process_plot_format
    'Unrecognized character %c in format string' % c)
ValueError: Unrecognized character a in format string

Expected outcome

A plot with a point at (0, 1)

Matplotlib version

(installed using conda)

• Operating system: Centos7
• Matplotlib version: 3.0.1
• Matplotlib backend: agg (but probably doesn't matter)
• Python version: 3.7
• Pandas version: 0.23.4

[ImportanceOfBeingErnest]

Bisects to #10872

[anntzer]

Fixed by #10928, which is opened since 8 months ago.

[stilley2]

Ah I missed that issue while searching. Should I close this one then?

[anntzer]

Well, that PR is not merged yet (I'm just gently nudging other devs to merge it...), so this can stay open until one of the fixing PRs goes in.

[timhoffm]

Will be fixed for 3.1 via #10928