Python图例属性错误 [英] Python legend attribute error

问题描述

为什么我在这里遇到与plt.plot标签有关的错误?

Why am I getting an error here that relates to the plt.plot label?

fig = plt.figure()
ax = plt.gca()
barplt = plt.bar(bins,frq,align='center',label='Dgr')
normplt = plt.plot(bins_n,frq_n,'--r', label='Norm');
ax.set_xlim([min(bins)-1, max(bins)+1])
ax.set_ylim([0, max(frq)])
plt.xlabel('Dgr')
plt.ylabel('Frequency')
plt.show()
plt.legend(handles=[barplt,normplt])

这是我得到的错误: 列表"对象没有属性"get_label"

This is the error that I get: 'list' object has no attribute 'get_label'

推荐答案

因为plt.plot可以一次绘制多条线，所以即使您仅绘制一条线(例如，在您的情况，长度为1)的列表.抓住图例的句柄时，您只想使用此列表的第一项(实际的line2D对象).

Because plt.plot can plot more than one line at once, it returns a list of line2D objects, even if you only plot one line (i.e. in your case, a list of length 1). When you grab its handle for the legend, you want to only use the first item of this list (the actual line2D object).

(至少)有两种方法可以解决此问题:

There are (at least) two ways you can resolve this:

1)调用plt.plot时，在normplt之后添加逗号，以便仅将列表中的第一项存储在normplt

1) add a comma after normplt when you call plt.plot, to only store the first item from the list in normplt

barplt = plt.bar(bins,frq,width,align='center',label='Dgr')
normplt, = plt.plot(bins_n,frq_n,'--r', label='Norm')   # note the comma after normplt

print normplt
# Line2D(Norm)    <-- This is the line2D object, not a list, so we can use it in legend
...
plt.legend(handles=[barplt,normplt])

2)调用plt.legend(normplt[0])时，仅使用列表中的第一项:

2) Use only the first item in the list when you call plt.legend (normplt[0]):

barplt = plt.bar(bins,frq,width,align='center',label='Dgr')
normplt = plt.plot(bins_n,frq_n,'--r', label='Norm')

print normplt
# [<matplotlib.lines.Line2D object at 0x112076710>]  
# Note, this is a list containing the Line2D object. We just want the object, 
# so we can use normplt[0] in legend
...
plt.legend(handles=[barplt,normplt[0]])

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