altair: NameError: name '_node' is not defined in altair/api.py:182

I am trying to save a png from altair with chart.savechart(filetype="eps", outfile="myfigure"). I have installed canvas with npm install canvas (I do not have conda). This command results in:

NameError                                 Traceback (most recent call last)
<ipython-input-9-7cc84e0f0694> in <module>()
----> 1 chart.savechart(filetype="eps", outfile="occupancy_vs_epoch")

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/altair/api.py in savechart(self, outfile, filetype)
    180                     f.write(self.to_html())
    181         else:
--> 182             supported = _node.SUPPORTED_FILETYPES + ['json', 'html']
    183             raise ValueError('Cannot save chart of type {0}; supported'
    184                              'extensions are {1}'.format(filetype, supported))

NameError: name '_node' is not defined

It seems _node is not mentioned anywhere else in this file. There is node variable though.

Version: ‘1.2.0’