[Matplotlib-users] bug with empty values & dates

[Jeffrey M. <jm...@gm...>]

I'm graphing data from a web service, and seem to have stumbled upon a
bug when dates are graphed without any values.

Here's a minimum repro:

import datetime
import matplotlib.pyplot as plt

fig = plt.figure()
ax = fig.add_subplot(111)

x = []
st = datetime.datetime(2012,11,21)
while st < datetime.datetime(2012,11,21, 16, 00):
    x.append(st)
    st = st + datetime.timedelta(minutes=30)
y = [None] * len(x)

ax.plot(x,y)
fig.autofmt_xdate()
plt.show()


The stack trace I get:

Traceback (most recent call last):
  File "min_mpl.py", line 15, in <module>
    fig.autofmt_xdate()
  File "c:\python26\lib\site-packages\matplotlib\figure.py", line 318,
in autofmt_xdate
    for label in ax.get_xticklabels():
  File "c:\python26\lib\site-packages\matplotlib\axes.py", line 2507,
in get_xticklabels
    self.xaxis.get_ticklabels(minor=minor))
  File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1104,
in get_ticklabels
    return self.get_majorticklabels()
  File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1088,
in get_majorticklabels
    ticks = self.get_major_ticks()
  File "c:\python26\lib\site-packages\matplotlib\axis.py", line 1186,
in get_major_ticks
    numticks = len(self.get_major_locator()())
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 749,
in __call__
    self.refresh()
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 758, in refresh
    dmin, dmax = self.viewlim_to_dt()
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 530,
in viewlim_to_dt
    return num2date(vmin, self.tz), num2date(vmax, self.tz)
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 289,
in num2date
    if not cbook.iterable(x): return _from_ordinalf(x, tz)
  File "c:\python26\lib\site-packages\matplotlib\dates.py", line 203,
in _from_ordinalf
    dt = datetime.datetime.fromordinal(ix)
ValueError: ordinal must be >= 1

Adding a 0 & the current date stops getting the exception, but the
range seems wildly messed up. (2011 - 2014).