[FIXED] How to detect if a twin axis has been generated for a matplotlib axis

Issue

How can one detect if an axis has a twin axis written on top of it? For example, if given ax below, how can I discover that ax2 exists?

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 2, 3])
ax2 = ax.twinx()

Solution

I don't think there's any built-in to do this, but you could probably just check whether any other axes in the figure has the same bounding box as the axes in question. Here's a quick snippet that will do this:

def has_twin(ax):
    for other_ax in ax.figure.axes:
        if other_ax is ax:
            continue
        if other_ax.bbox.bounds == ax.bbox.bounds:
            return True
    return False

# Usage:

fig, ax = plt.subplots()
print(has_twin(ax))  # False

ax2 = ax.twinx()
print(has_twin(ax))  # True

Answered By - jakevdp