Utility function to use with matplotlib.pyplot to put a mirrored y-axis on the right of the plot. Uses state of pyplot to determine appropriate axes.

mirror.py

import matplotlib.pyplot as plt
import matplotlib.ticker as tk

def Mirror(prec=1):
    """Adds y-axis that's a mirror of the y-axis on left.

    Parameters
    ----------
    prec : int (opt) Default=1
        Number of significant digits (precision) to use on scale
    Notes
    -----
    Use this function just before the final fig.show() command.
    """
    ax = plt.gca()
    ax2 = ax.twinx()
    fmt = '% .{}f'.format(prec) # adds a space if number is >0
    ax.yaxis.set_major_formatter(tk.FormatStrFormatter(fmt))
    ax2.yaxis.set_major_formatter(tk.FormatStrFormatter(fmt))
    ax2.grid(False) # is sitting on top of lines
    ax2.set_yticks(ax.get_yticks())
    ax2.set_ylim(ax.get_ylim())