matplotlib: legend()

base knowledge:

def legend(*args, **kwargs):

    ret = gca().legend(*args, **kwargs)
    return ret

#if (len(args)==2)  then the args mean the set of [artist] and [label]

# if (len(args==0)  then  it will equal handles,labels= ax.get_legend_handles_labels()

#                                        ax.legend(handles,labels)  #the sentence will get 

# from ax.labels,ax.patch and LinCollection or RegularPolyCollection

1.1 adjust the order    

ax = subplot(1,1,1)
p1, = ax.plot([1,2,3], label="line 1")
p2, = ax.plot([3,2,1], label="line 2")
p3, = ax.plot([2,3,1], label="line 3")
handles, labels = ax.get_legend_handles_labels()
ax.legend(handles[::-1],labels[::-1])   #reverse the order

# sort them by labels

import operatorhl= sorted(zip(handles,labels),key=operator.itemgetter(1))

handles2,labels2=zip(*hl)

ax.legend(handles2,labels2)

1.2 use agency artist

    if using legend doesn't support artist,we can use another artist which is supported by other legend

 for example:

    p=Rectangle((o,o),1,1,fc='r')

    legend([p],["Red Rectangle"])

2.multiseriate legend:
 

  
  
ax1 = plt.subplot(2,1,1)
  
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(2,1,2)
  
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. set location of legend
 
 

  

   
  
  

 
 

4.many legends

from matplotlib.pyplot import * p1, = plot([1,2,3], label="test1")
p2, = plot([3,2,1], label="test2")
l1 = legend([p1], ["Label 1"], loc=1)l2 = legend([p2], ["Label 2"], 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)
parent --- 
       ±ÈÈçÓÃax.legend()µ÷ÓÃÖ®ºó
       >>> print ax.get_legend().parent
       Axes(0.125,0.1;0.775x0.8)
handles --- artist（lines, patches）
labels --- labels of artist 
Other parameter:

Keyword	Description
loc	a location code
prop	the font property (matplotlib.font_manager.FontProperties ¶ÔÏó) eg song_font = matplotlib.font_manager.FontProperties(fname='simsun.ttc', size=8)
fontsize	the font size (ºÍprop»¥³â，²»¿ÉͬʱʹÓÃ)
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.

main fuction:

get_frame() ---

get_lines()

get_patches()

get_texts()

get_title() ---

set_bbox_to_anchor(bbox, transform=None)

Reference:

http://blog.sina.com.cn/s/blog_4b9acb520101an32.html

http://www.cnblogs.com/yinheyi/p/6792120.html