Matplotlib savefig 带有图外的图例

Question

阅读下面的文章，我设法把一个传说放在情节之外。

• How to put the legend out of the plot

代码：

import matplotlib.pyplot as pyplot

x = [0, 1, 2, 3, 4]
y = [xx*xx for xx in x]

fig = pyplot.figure()
ax  = fig.add_subplot(111)

box = ax.get_position()
ax.set_position([box.x0, box.y0, box.width*0.8, box.height])

ax.plot(x, y)
leg = ax.legend(['abc'], loc = 'center left', bbox_to_anchor = (1.0, 0.5))
#pyplot.show()

fig.savefig('aaa.png', bbox_inches='tight')

pyplot.show() 显示正确的图，其外带有图例。但是当我将它保存为带有fig.savefig() 的文件时，图例会被截断。

一些谷歌搜索向我展示了解决方法，例如将 bbox_extra_artists=[leg.legendPatch] 或 bbox_extra_artists=[leg] 添加到 savefig()，但都没有奏效。

正确的做法是什么？ Matplotlib 版本为 0.99.3。

谢谢。

Answer 1

问题在于，当您动态绘制时，matplotlib 会自动确定边框以适合您的所有对象。 当您保存文件时，事情不会自动完成，因此您需要指定 图形的大小，然后是坐标区对象的边界框。 以下是如何更正您的代码：

import matplotlib.pyplot as pyplot

x = [0, 1, 2, 3, 4]
y = [xx*xx for xx in x]

fig = pyplot.figure(figsize=(3,3))
ax  = fig.add_subplot(111)

#box = ax.get_position()
#ax.set_position([0.3, 0.4, box.width*0.3, box.height])
# you can set the position manually, with setting left,buttom, witdh, hight of the axis
# object
ax.set_position([0.1,0.1,0.5,0.8])
ax.plot(x, y)
leg = ax.legend(['abc'], loc = 'center left', bbox_to_anchor = (1.0, 0.5))

fig.savefig('aaa.png')

Answer 2

虽然这种方法适用于图例，但当有多个子图并且我们想要一个整体图例时，它似乎不适用于 figlegend。 figlegend 在 savefig 时仍然会被裁剪。我只是在下面粘贴了我的临时解决方案，以防有人遇到这种情况。

import matplotlib.pyplot as plt

para = {
    ## this parameter will indicate the position of
    ## subplot within figure, but will not be shown
    ## if using bbox_inches='tight' when saving
    'figure.subplot.top': 0.5
}
#plt.rcParams.update(para)

fig = plt.figure()

ax=fig.add_subplot(221)
## only needed when what to manually control
## subplot ration
#ax.set_position([0.1,0.6,0.5, 0.4])
ax.plot([1,1,1])


ax=fig.add_subplot(222)
#ax.set_position([0.7,0.6,0.5, 0.4])
ax.plot([2,2,2])

ax=fig.add_subplot(223)
#ax.set_position([0.1,0.1,0.5, 0.4])
ax.plot([3,3,3])


ax=fig.add_subplot(224)
#ax.set_position([0.7,0.1,0.5, 0.4])
p1, = ax.plot([4,4,4])
p2, = ax.plot([2,3,2])

## figlegend does not work fine with tight bbox
## the legend always get cropped by this option
## even add bbox extra will not help
## had to use legend, and manually adjust it to
## arbitary position such as (0.3, 2.5)

## http://matplotlib.org/users/tight_layout_guide.html
## according to this link, tight layout is only
## an experimental feature, might not support figlegend

#lgd = plt.figlend(
lgd = plt.legend(
    [p1,p2],
    ['a', 'b'],
    ## by default, legend anchor to axis, but can
    ## also be anchored to arbitary position
    ## positions within [1,1] would be within the figure
    ## all numbers are ratio by default

    bbox_to_anchor=(-0.1, 2.5),

    ## loc indicates the position within the figure
    ## it is defined consistent to the same Matlab function 
    loc='center',

    ncol=2
    #mode="expand",
    #borderaxespad=0.
    )



#plt.show()

plt.savefig('temp.png', bbox_inches='tight')#, bbox_extra_artist=[lgd])

Answer 3

如果一切都失败了，我会使用 Inkscape 的边界框功能来处理我所说的 matplotlib 输出中的持久性错误。如果您正在运行 GNU/Linux，只需将 Matplotlib 提供的任何内容保存为 pdf，然后将其发送到以下位置

def tightBoundingBoxInkscape(pdffile,use_xvfb=True):
    """Makes POSIX-specific OS calls. Preferably, have xvfb installed, to avoid any GUI popping up in the background. If it fails anyway, could always resort to use_xvfb=False, which will allow some GUIs to show as they carry out the task 
      pdffile: the path for a PDF file, without its extension
    """
    usexvfb='xvfb-run '*use_xvfb
    import os
    assert not pdffile.endswith('.pdf')
    os.system("""
       inkscape -f %(FN)s.pdf -l %(FN)s_tmp.svg
       inkscape -f %(FN)s_tmp.svg --verb=FitCanvasToDrawing \
                                   --verb=FileSave \
                                   --verb=FileQuit
      inkscape -f %(FN)s_tmp.svg -A %(FN)s-tightbb.pdf
"""%{'FN':pdffile}