legend显示图例
1 legend基础
函数原型legend(*args, **kwargs)
当len(args) == 2
args是[artist]和[label]的集合
当len(args) == 0
args会自动调用get_legend_handles_labels()生成
等价于
handles, labels = ax.get_legend_handles_labels()
ax.legend(handles, labels)
ax.get_legend_handles_labels()的作用在于返回ax.lines, ax.patch所有对象以及ax.collection中的LineCollectionorRegularPolyCollection对象
注意：这里只提供有限支持,并不是所有的artist都可以被用作图例，比如errorbar支持不完善
1.1调整顺序
ax=subplot(1,1,1)
p1,=ax.plot([1,2,3], label="line1")
p2,=ax.plot([3,2,1], label="line2")
p3,=ax.plot([2,3,1], label="line3")
handles, labels=ax.get_legend_handles_labels()
# reverse the order
ax.legend(handles[::-1], labels[::-1])
# or sort them by labels
importoperatorhl=sorted(zip(handles,labels), key=operator.itemgetter(1))
handles2, labels2=zip(*hl)
ax.legend(handles2, labels2)
1.2使用代理artist
当需要使用legend不支持的artist时，可以使用另一个被legend支持的artist作为代理
比如以下示例中使用不在axe上的一个artist
p=Rectangle((0,0), 1, 1,fc="r")
legend([p], ["RedRectangle"])
2多列图例
ax1=plt.subplot(3,1,1)
ax1.plot([1], label="multinline")
ax1.plot([1], label="$2^{2^2}$")
ax1.plot([1], label=r"$frac{1}{2}pi$")
ax1.legend(loc=1, ncol=3, shadow=True)
ax2=plt.subplot(3,1,2)
myplot(ax2)
ax2.legend(loc="center left", bbox_to_anchor=[0.5,0.5],
ncol=2, shadow=True, title="Legend")
ax2.get_legend().get_title().set_color("red")
3图例位置
ax.legend(…., loc=3)具体对应位置如下图
绘制在图上是这样的，（具体没有分清5和7的区别）
4多个图例
如果不采取措施，连续调用两个legend会使得后面的legend覆盖前面的
frommatplotlib.pyplotimport*p1,=plot([1,2,3], label="test1")
p2,=plot([3,2,1], label="test2")
l1=legend([p1], ["Label1"],loc=1)l2=legend([p2], ["Label2"],loc=4)# this removes l1 from the axes.
gca().add_artist(l1)# add l1 as a separate artist to the axes
5. API
class matplotlib.legend.Legend(parent,handles, labels,**args)
三个最重要的必要参数
parent --- legend的父artist， 包含legend的对象
比如用ax.legend()调用之后
>>> print ax.get_legend().parent
Axes(0.125,0.1;0.775x0.8)
handles ---图例上面画出的各个artist（lines, patches）
labels --- artist对应的标签
其他参数
Keyword
Description
loc
a location code
prop
the font property (matplotlib.font_manager.FontProperties对象)
eg
song_font = matplotlib.font_manager.FontProperties(fname='simsun.ttc', size=8)
fontsize
the font size (和prop互斥，不可同时使用)
markerscale
the relative size of legend markers vs. original
numpoints
the number of points in the legend for line
scatterpoints
the number of points in the legend for scatter plot
scatteryoffsets
a list of yoffsets for scatter symbols in legend
frameon
if True, draw a frame around the legend. If None, use rc
fancybox
if True, draw a frame with a round fancybox. If None, use rc
shadow
if True, draw a shadow behind legend
ncol
number of columns
borderpad
the fractional whitespace inside the legend border
labelspacing
the vertical space between the legend entries
handlelength
the length of the legend handles
handleheight
the length of the legend handles
handletextpad
the pad between the legend handle and text
borderaxespad
the pad between the axes and legend border
columnspacing
the spacing between columns
title
the legend title
bbox_to_anchor
the bbox that the legend will be anchored.
bbox_transform
the transform for the bbox. transAxes if None.
主要函数
get_frame() ---返回legend所在的方形对象
get_lines()
get_patches()
get_texts()
get_title() ---上面几个比较简单，不解释了
set_bbox_to_anchor(bbox, transform=None)
(…本函数待续…之后写axes的时候会加入，目前我没有看懂他的这个长宽和figure以及axes的关系)
6.样例
leg=ax.legend(('Model length','Data length','Total message length'),
'upper center', shadow=True)
# the matplotlib.patches.Rectangle instance surrounding the legend即外框
frame=leg.get_frame()
frame.set_facecolor('0.80')# set the frame face color to light gray
# matplotlib.text.Text instances即legend中文本
fortinleg.get_texts():
t.set_fontsize('small')# the legend text fontsize
# matplotlib.lines.Line2D instances即legend中所表示的artist
forlinleg.get_lines():
l.set_linewidth(1.5)# the legend line width
fig=plt.figure()
ax1=fig.add_axes([0.1,0.1,0.4,0.7])
ax2=fig.add_axes([0.55,0.1,0.4,0.7])
x=np.arange(0.0,2.0,0.02)
y1=np.sin(2*np.pi*x)
y2=np.exp(-x)
l1, l2=ax1.plot(x, y1,'rs-', x, y2,'go')
y3=np.sin(4*np.pi*x)
y4=np.exp(-2*x)
l3, l4=ax2.plot(x, y3,'yd-', x, y3,'k^')
fig.legend((l1, l2), ('Line 1','Line 2'),'upper left')
fig.legend((l3, l4), ('Line 3','Line 4'),'upper right')
原文参考：http://blog.sina.com.cn/s/blog_b09d460201019c10.html
