Ways to combine legends in matplotlib

legend.py

def combined_legend(*axes):
    """Creates combines legends from provided axes.
    
    Usually used for ax and ax.twinx()
    """
    lines, labels = [], []
    for ax in axes:
        line, label = ax.get_legend_handles_labels()
        lines.extend(line)
        labels.extend(label)
    ax.legend(lines, labels)

# E.g., combined_legend(ax, ax.twinx())

# Or use a figure caption in mpl >= 2.1
# https://stackoverflow.com/a/47370214/1612867

# In general, position specified by loc should match bbox_to_anchor
# in terms of its relative position (upper left, upper right, etc.)

# Upper right
plt.gcf().legend(loc=1, bbox_to_anchor=(1,1), bbox_transform=ax.transAxes);
# Upper left
plt.gcf().legend(loc=2, bbox_to_anchor=(0,1), bbox_transform=ax.transAxes);