matplotlib：同时绘制到不同的图

Question

Due to the 2nd answer of this question I supposed the following code

import matplotlib.pyplot as plt

for i1 in range(2):

    plt.figure(1)
    f, ax = plt.subplots()
    plt.plot((0,3), (2, 2), 'b')


    for i2 in range(2):
        plt.figure(2)
        f, ax = plt.subplots()
        plt.plot([1,2,3], [1,2,3], 'r')
        plt.savefig('foo_{}_bar_{}.jpg'.format(i2, i1))
        plt.close()

    plt.figure(1)
    plt.plot( [1,2,3],[1,2,3], 'r')

    plt.savefig('bar_{}.jpg'.format(i1))
    plt.close()

to create plots bar_0.jpg and bar_1.jpg showing a blue and a red line each.

However, figures look like

instead of

How can I achieve the desired behaviour? Note that plots foo_*.jpg have to be closed and saved during handling of the bar plots.

Answer 1

You're already saving the Axes objects, so instead of calling the PyPlot plot function (which draws on the last created or activated Axes ), use the objects' plot function:

ax.plot(...)

If you then give both a different name, say ax1 and ax2 , you can draw on the one you like without interfering with the other. All plt. commands also exist as an Axes member function, but sometimes the name changes ( plt.xticks becomes ax.set_xticks for example). See the documentation of Axes for details.

To save to figures, use the Figure objects in the same way:

f.savefig(...)

This API type is only just coming to Matlab, FYI, and will probably replace the old-fashioned "draw on the last active plot" behaviour in the future. The object-oriented approach here is more flexible with minimal overhead, so I strongly recommend you use it everywhere.

Answer 2

If unsure, better to make it explicit:

import matplotlib.pyplot as plt

for i1 in range(2):
    fig1,ax1 = plt.subplots()
    fig2,ax2 = plt.subplots()
    ax1.plot([0,4],[2,2],'b')

for i2 in range(2):
    ax2.plot([1,2,3],[1,2,3],'r')
    fig2.savefig('abc{}.png'.format(2*i1+i2))
    plt.figure(1)
    ax1.plot([1,2,3],[1,2,3],'r')

fig1.savefig('cba{}.png'.format(i1))