How to monkey patch matplotlib's axis safely (Not affecting future calls)?

Question

I have a function which visualizes matrix elements using bar3d. I was trying to remove margins at the bounding limits of z-axis. I found this answer(first one) which uses monkey patching. So my code looks like this:

from mpl_toolkits.mplot3d import Axes3D
from mpl_toolkits.mplot3d.axis3d import Axis

# function which applies monkey patching
def _remove_margins():
    """
    Removes margins about z=0 and improves the style
    """
    if not hasattr(Axis, "_get_coord_info_old"):
        def _get_coord_info_new(self, renderer):
            mins, maxs, centers, deltas, tc, highs = \
                self._get_coord_info_old(renderer)
            mins += deltas/4
            maxs -= deltas/4
            return mins, maxs, centers, deltas, tc, highs
        Axis._get_coord_info_old = Axis._get_coord_info
        Axis._get_coord_info = _get_coord_info_new


# function which visualizes the matrix
# ✅ this function should be affected by monkey patching
def visualize_matrix(M, figsize, ... ):
    _remove_margins()
    
    fig = plt.figure(figsize=figsize)
    ax  = Axes3D(fig)
    ax.bar3d(...)
    .
    .
    .
    return fig, ax

# another function that uses Axes3D
# ⛔️ this function should not be affected by monkey patching
def visualize_sphere(...):
    fig = plt.figure(figsize=figsize)
    ax  = Axes3D(fig)
    .
    .
    .
    return fig, ax

Problem:

In future calls of Axes3D (e.g. using visualize_sphere function) the changes made by monkey patching still remains.

Question:

How to monkey patch safely to solve the problem?

`__enter__` should do the monkey-patching if necessary, and save off a bool representing whether or not it did any work. `__exit__` should restore those functions to their original state *if* `__enter__` made any changes. — 0x5453, Jun 17 '21 at 18:19
The various `patch` decorators in `unittest.mock` can also be used as context managers. — chepner, Jun 17 '21 at 18:28
Monkey-patching is generally not going to be a safe procedure. — user2357112, Jun 20 '21 at 01:04

umitu · Accepted Answer · 2021-07-17T23:24:54.790

I changed the monkey patch to make changes only to the instance, not the class. Apply patch_axis to ax.xaxis, ax.yaxis and ax.zaxis after creating the ax.

import matplotlib.pyplot as plt
import numpy as np


def patch_axis(axis):
    def _get_coord_info_new(renderer):
        mins, maxs, centers, deltas, tc, highs = _get_coord_info_old(renderer)
        mins += deltas / 4
        maxs -= deltas / 4
        return mins, maxs, centers, deltas, tc, highs

    _get_coord_info_old = axis._get_coord_info
    axis._get_coord_info = _get_coord_info_new


def test():
    fig = plt.figure()
    ax = fig.add_subplot(111, projection='3d')
    ax.margins(0)
    for c, z in zip(['r', 'g', 'b', 'y'], [30, 20, 10, 0]):
        xs = np.arange(20)
        ys = np.random.rand(20)

        # You can provide either a single color or an array. To demonstrate this,
        # the first bar of each set will be colored cyan.
        cs = [c] * len(xs)
        cs[0] = 'c'
        ax.bar(xs, ys, zs=z, zdir='y', color=cs, alpha=0.8)

    ax.set_xlabel('X')
    ax.set_ylabel('Y')
    ax.set_zlabel('Z')

    return fig, ax

# without the margin
fig, ax = test()
patch_axis(ax.xaxis)
patch_axis(ax.yaxis)
patch_axis(ax.zaxis)
fig.savefig("test1.png")

# with the margin
fig, ax = test()
fig.savefig("test2.png")

Methods are just functions defined in the namespace of classes, and accessing instance method implicitly fill in the self parameters (see Class instances in https://docs.python.org/3/reference/datamodel.html). You can override the bound method by assigning functions without self parameters in the namespaces the instantiation adds.

>>> class C:
...     def f(self): return 1
... 
>>> C.f
<function C.f at 0x7f36a7eb53a0>
>>> c = C()
>>> c.f
<bound method C.f of <__main__.C object at 0x7f36a7f48eb0>>
>>> c.f()
1
>>> c.f = lambda: 2
>>> c.f()
2

thanks, yes it works for your case where the function uses `plt.show()`. In my case the functions return `fig` and `ax` (no `plt.show()` is used) and I want to use patching inside of the function. `with Patch(): return fig, ax` is not working — Mehdi, Jun 20 '21 at 14:13
Very nice, so the conclusion is that monkey patching to remove the margins could be done safely (i.e. not affecting future calls) without using a `with` statement? Maybe I have to change the question! — Mehdi, Jun 20 '21 at 17:08

How to monkey patch matplotlib's axis safely (Not affecting future calls)?

Problem:

Question:

1 Answers1