from ggplot import *
import matplotlib.pyplot as plt
plt.figure()
ggplot(aes(x='date_hour', y='pageviews'), data=pageviews) + \
    geom_point() +\
    geom_hline(yintercept=[10000])

Traceback (most recent call last):
  File "/home/user/anaconda2/envs/myenv/lib/python3.5/code.py", line 91, in runcode
    exec(code, self.locals)
  File "<input>", line 3, in <module>
  File "/home/user/anaconda2/envs/myenv/lib/python3.5/site-packages/ggplot/ggplot.py", line 116, in __repr__
    self.make()
  File "/home/user/anaconda2/envs/myenv/lib/python3.5/site-packages/ggplot/ggplot.py", line 636, in make
    layer.plot(ax, facetgroup, self._aes, **kwargs)
  File "/home/user/anaconda2/envs/myenv/lib/python3.5/site-packages/ggplot/geoms/geom_hline.py", line 36, in plot
    ax.axhline(y, **params)
  File "/home/user/anaconda2/envs/myenv/lib/python3.5/site-packages/matplotlib/axes/_axes.py", line 722, in axhline
    scaley = (yy < ymin) or (yy > ymax)
TypeError: unorderable types: float() > NoneType()