The pie wedges are approximated using a 72-sided polygon (each side 5
degrees), rather than a true ellipse. There is a bug that if the wedge
is smaller than a half of a side of this polygon (2.5 degrees) it
creates only one side of the wedge.
This has been fixed on the 0.91.x maintenance branc
It looks like pie() omits slices that are smaller than a few percent.
In the following example, only one pie slice is drawn:
>>> import pylab
>>> pylab.pie([98,2])
>>> pylab.show()
The missing pie slice has neither a color fill nor a boundary (the
arc of the pie slice is missing).
By contrast,
