Question

Previously, I had a problem with the interference between multiple Matplotlib figures. Finally i got tracked that to an issue that some pyplot functions do not attach to their figure instance but can be rendered in some other figure instances which are created in parallel.

Here is some example code:

from django.http import HttpResponse
from numpy import arange, meshgrid
from matplotlib.mlab import bivariate_normal

def show_chart(request):
    delta = 0.025
    x = arange(-3.0, 3.0, delta)
    y = arange(-2.0, 2.0, delta)
    X, Y = meshgrid(x, y)
    Z1 = bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
    Z2 = bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
    Z = 10.0 * (Z2 - Z1)

    from matplotlib.pyplot import figure, contour
    fig1 = figure(figsize=(4, 4), facecolor='white')
    contour(X, Y, Z)

    response = HttpResponse(content_type='image/png')
    fig1.savefig(response, format='png')
    fig1.clear()
    return response

The contour pyplot function in the example above can get rendered in fig1, but occasionally also in some other figure that is generated in parallel. That is very annoying. Is there any way to attach the contour pyplot function to fig1?

Answer 1

You can create a subplot and than call the contour method of the subplot:

fig1 = figure(figsize=(4, 4), facecolor='white')
ax = fig1.add_subplot(111)
ax.contour(X, Y, Z)

plt.subplots makes it convenient to create a figure and subplots with a single call:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()