使用numpy将范围设置为零(Setting ranges to zero using numpy)

 我开始使用numpy cookbook独立学习numpy。 我查看并执行了以下代码： 
 
import scipy.misc
import matplotlib.pyplot

#This script demonstates fancy indexing by setting values
#On the diagnols to 0

#Load lena array
lena = scipy.misc.lena()
xmax = lena.shape[0]
ymax = lena.shape[1]

#Fancy indexing
#can set ranges of points to zero, all at once instead of using loop
lena[range(xmax), range(ymax)] = 0
lena[range(xmax-1,-1,-1), range(ymax)] = 0
matplotlib.pyplot.imshow(lena)
matplotlib.pyplot.show()
 
 我理解这段代码中的所有内容除外： 
 
lena[range(xmax), range(ymax)] = 0
lena[range(xmax-1,-1,-1), range(ymax)] = 0
 
 我阅读了关于索引和切片的文档 ，但仍然无法理解上面的代码。 以下是我的困惑点： 
 
 1）范围（xmax）和范围（ymax）包括整个x，y轴。 将它们设置为零会使整个图像变黑吗？ 

 2）范围（xmax-1，-1，-1）是什么意思？ 
 
 多谢你们！ 

I began independently learning numpy using the numpy cookbook. I reviewed and executed the following code:
 
import scipy.misc
import matplotlib.pyplot

#This script demonstates fancy indexing by setting values
#On the diagnols to 0

#Load lena array
lena = scipy.misc.lena()
xmax = lena.shape[0]
ymax = lena.shape[1]

#Fancy indexing
#can set ranges of points to zero, all at once instead of using loop
lena[range(xmax), range(ymax)] = 0
lena[range(xmax-1,-1,-1), range(ymax)] = 0
matplotlib.pyplot.imshow(lena)
matplotlib.pyplot.show()
 
I understand everything in this code except:
 
lena[range(xmax), range(ymax)] = 0
lena[range(xmax-1,-1,-1), range(ymax)] = 0
 
I read the documentation on indexing and slicing but still cannot make sense of the above code. Here is are my points of confusion:
 
1)range(xmax) and range(ymax) encompass the entire x,y axes. Wouldn't setting them to zero make the entire image black?

 2)What does range(xmax-1,-1,-1) mean?
 
Thanks guys!

原文：https://stackoverflow.com/questions/21971483