You are reading an old version of the documentation (v2.0.2). For the latest version see https://matplotlib.org/stable/api/_as_gen/matplotlib.axes.Axes.set_ymargin.html
matplotlib

Travis-CI:

This Page

matplotlib.axes.Axes.set_ymargin

Axes.set_ymargin(m)

Set padding of Y data limits prior to autoscaling.

m times the data interval will be added to each end of that interval before it is used in autoscaling.

accepts: float in range 0 to 1