class Power(object):
    def __init__(self, power):
        self.power = power

%matplotlib inline

import numpy as np
from IPython.core.pylabtools import print_figure
import matplotlib.pyplot as plt

def power_png(p):
    fig, ax = plt.subplots()
    x = np.linspace(-5,5)
    y = x ** p.power
    ax.plot(x,y)
    buf = print_figure(fig, 'png')
    plt.close(fig) # close the figure
    return buf
    

p = Power(5)

df = get_ipython().display_formatter
png = df.formatters['image/png']
png.for_type(Power, power_png)