在python中的2D列表（矩阵）范围内进行迭代

Question

I would like to iterate over a 2D list. I understand that I can do this with:

for j in range(columns):
     for i in range(rows):
        print depth[i][j],

But is there a more beautiful way. I tried:

for (x in range(rows)) and (y in range(columns)):
     print(depth[x][y])

But this given me an IndentationError .:

Thanks

EDIT: what if i want to set bounds for x and y. Say I have a 4x4 matrix(using list to represent it). For a given element I want to get 3x3 matrix around it, but i want to remain within the bounds of the original matrix. Suppose I am at (3,1), taking x = range(3-2, 3+3) = [1,2,3,4,5] and y = range(1-2,1+3) = [-1, 0, 1, 2, 3] would take me outside the bounds of the original matrix.

Answer 1

You can use itertools.product , or write a double-loop generator-expression like:

for (i,j) in ( (i,j) for i in range(rows) for j in range(columns) ):
    print depth[i][j]

or

for d in ( depth[i][j] for i in range(rows) for j in range(columns) ): ...

also, if you don't actually need the indices, but only to iterate over the values of depth , you can do:

for row in depth:
   for v in row:
      print

and even if you do need the indices, it is more pythonic to use enumerate :

for row_index, row in enumerate(depth):
   for col_index, v in enumerate(row):
      print 'depth[%d][%d]=%s' % (row_index, col_index, v)

Answer 2

This can be done with:

for depth in (depth[x][y] for x in range(rows) for y in range(columns)):
    print depth

Edit:

If you want bounds you can use the min and max builtins :

for x in range( max(x_min,col-2), min(x_max,col+3) ):
    #do stuff