Come si crea una legenda per un tracciato del contorno in matplotlib?

Question

Non riesco a trovare la risposta da nessuna parte! Ho trovato una discussione here, ma provare questo ho una TypeError: 'NoneType' object is not iterable:

>>> import numpy as np 
>>> import matplotlib.pyplot as plt 
>>> x, y = np.meshgrid(np.arange(10),np.arange(10)) 
>>> z = x + y 
>>> cs = plt.contourf(x,y,z,levels=[2,3]) 
>>> cs.collections[0].set_label('test') 
>>> plt.legend() 
Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/pyplot.py", line 2791, in legend 
    ret = gca().legend(*args, **kwargs) 
    File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/axes.py", line 4475, in legend 
    self.legend_ = mlegend.Legend(self, handles, labels, **kwargs) 
    File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/legend.py", line 365, in __init__ 
    self._init_legend_box(handles, labels) 
    File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/legend.py", line 627, in _init_legend_box 
    handlebox) 
    File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/legend_handler.py", line 110, in __call__ 
    handlebox.get_transform()) 
    File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/legend_handler.py", line 352, in create_artists 
    width, height, fontsize) 
    File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/legend_handler.py", line 307, in get_sizes 
    size_max = max(orig_handle.get_sizes())*legend.markerscale**2 
TypeError: 'NoneType' object is not iterable 

EDIT: Sto cercando qualcosa di simile a questo:

Answer 1

È possibile creare gli artisti del proxy per fare la leggenda:

import numpy as np 
import matplotlib.pyplot as plt 
x, y = np.meshgrid(np.arange(10),np.arange(10)) 
z = np.sqrt(x**2 + y**2) 
cs = plt.contourf(x,y,z,levels=[2,3,4,6]) 

proxy = [plt.Rectangle((0,0),1,1,fc = pc.get_facecolor()[0]) 
    for pc in cs.collections] 

plt.legend(proxy, ["range(2-3)", "range(3-4)", "range(4-6)"]) 
plt.show() 

Answer 2

Si potrebbe anche farlo direttamente con le linee del contorno, senza utilizzare proxy artist.

import matplotlib 
import numpy as np 
import matplotlib.cm as cm 
import matplotlib.mlab as mlab 
import matplotlib.pyplot as plt 

matplotlib.rcParams['xtick.direction'] = 'out' 
matplotlib.rcParams['ytick.direction'] = 'out' 

delta = 0.025 
x = np.arange(-3.0, 3.0, delta) 
y = np.arange(-2.0, 2.0, delta) 
X, Y = np.meshgrid(x, y) 
Z1 = mlab.bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0) 
Z2 = mlab.bivariate_normal(X, Y, 1.5, 0.5, 1, 1) 
# difference of Gaussians 
Z = 10.0 * (Z2 - Z1) 



# Create a simple contour plot with labels using default colors. The 
# inline argument to clabel will control whether the labels are draw 
# over the line segments of the contour, removing the lines beneath 
# the label 
plt.figure() 
CS = plt.contour(X, Y, Z) 
plt.clabel(CS, inline=1, fontsize=10) 
plt.title('Simplest default with labels') 

labels = ['line1', 'line2','line3','line4', 
      'line5', 'line6'] 
for i in range(len(labels)): 
    CS.collections[i].set_label(labels[i]) 

plt.legend(loc='upper left') 

produrrà:

Tuttavia, si potrebbe anche voler esaminare le annotazioni per il proprio bisogno. A mio parere vi darà un maggiore controllo a grana fine su dove e ciò che si scrive sull'immagine, qui è lo stesso esempio con qualche annotazione:

### better with annotation, more flexible 
plt.figure(2) 
CS = plt.contour(X, Y, Z) 
plt.clabel(CS, inline=1, fontsize=10) 
plt.title('Simplest default with labels') 

plt.annotate('some text here',(1.4,1.6)) 
plt.annotate('some text there',(-2,-1.5))