Identity line for matplotlib

matplotlib_identity_line.py

import matplotlib.pyplot as plt

def identity_line(ax=None, ls='--', *args, **kwargs):
    # see: https://stackoverflow.com/q/22104256/3986320
    ax = ax or plt.gca()
    identity, = ax.plot([], [], ls=ls, *args, **kwargs)
    def callback(axes):
        low_x, high_x = ax.get_xlim()
        low_y, high_y = ax.get_ylim()
        low = min(low_x, low_y)
        high = max(high_x, high_y)
        identity.set_data([low, high], [low, high])
    callback(ax)
    ax.callbacks.connect('xlim_changed', callback)
    ax.callbacks.connect('ylim_changed', callback)
    return ax