Re: [Matplotlib-users] bug with empty values & dates

[Goyo <goy...@gm...>]

2012/11/22 Jeffrey Melloy <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).

I can't figure out what's going on here, the calls in the stack trace
seem unrelated to Y data.
As a quick and dirty workaround you can set the first and last Y
values to 0 --won't work well if you use markers.

Goyo