[matplotlib-devel] autofmt_xdate() broken for twinx()

[Scott S. <sco...@gm...>]

Hi,

It seems that the autofmt_xdate helper method is broken when twinx is
used. Consider the script below:

-----------------------------------------
import datetime as dt

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.dates import date2num

strt = dt.datetime(2000, 3, 15, 6)
delta = dt.timedelta(hours=6)
date_list = [(strt + i*delta) for i in range(100)]

x = date2num(date_list)
y = np.sin(x)
z = np.cos(x)

fig, ax1 = plt.subplots()

ax1.plot(date_list, y, 'b-')

ax2 = ax1.twinx()
ax2.plot(date_list, z, 'r-')

# using the auto format method doesn't work
fig.autofmt_xdate()

plt.show()
-----------------------------------------

This is because the 'is_last_row' attribute isn't present on ax2 and
len(fig.axes) != 1 when the autofmt_xdate method is called on fig.

The attached patch fixes it for me and still seems to give the
advertised behaviour for single and vertically stacked subplots.

Cheers,
Scott