a=[]
k=10
for r in range(7):
  a.append([])
 for c in range(7):
   a[r].append(k)
   k+=1
print(a[0]);print(a[1]);print(a[2]);print(a[3]);print(a[4]);print(a[5]);print(a[6])

def swap1(a):
    n = len(a)
    for i in range(n):
        a[i][i], a[n-i-1][i] = a[n-i-1][i], a[i][i]


def show(a):
    for r in a:
        print (', '.join(['{:2d}'.format(i) for i in r]))

a = [[j + i*7 + 1 for j in range(7)] for i in range(7)]

show(a)
swap1(a)
print()
show(a)

1,  2,  3,  4,  5,  6,  7
 8,  9, 10, 11, 12, 13, 14
15, 16, 17, 18, 19, 20, 21
22, 23, 24, 25, 26, 27, 28
29, 30, 31, 32, 33, 34, 35
36, 37, 38, 39, 40, 41, 42
43, 44, 45, 46, 47, 48, 49

43,  2,  3,  4,  5,  6, 49
 8, 37, 10, 11, 12, 41, 14
15, 16, 31, 18, 33, 20, 21
22, 23, 24, 25, 26, 27, 28
29, 30, 17, 32, 19, 34, 35
36,  9, 38, 39, 40, 13, 42
 1, 44, 45, 46, 47, 48,  7

In [98]: import numpy as np

In [99]: a = np.arange(1, 50).reshape(7, -1)

In [100]: print(a)
[[ 1  2  3  4  5  6  7]
 [ 8  9 10 11 12 13 14]
 [15 16 17 18 19 20 21]
 [22 23 24 25 26 27 28]
 [29 30 31 32 33 34 35]
 [36 37 38 39 40 41 42]
 [43 44 45 46 47 48 49]]

In [101]: a[np.diag_indices_from(a)], a[:, ::-1][np.diag_indices_from(a)] =
              np.fliplr(a).diagonal().copy(), a.diagonal().copy()

In [102]: print(a)
[[ 7  2  3  4  5  6  1]
 [ 8 13 10 11 12  9 14]
 [15 16 19 18 17 20 21]
 [22 23 24 25 26 27 28]
 [29 30 33 32 31 34 35]
 [36 41 38 39 40 37 42]
 [49 44 45 46 47 48 43]]

>>> import numpy as np
>>> a = np.arange(49).reshape(7, -1)
>>> a
array([[ 0,  1,  2,  3,  4,  5,  6],
       [ 7,  8,  9, 10, 11, 12, 13],
       [14, 15, 16, 17, 18, 19, 20],
       [21, 22, 23, 24, 25, 26, 27],
       [28, 29, 30, 31, 32, 33, 34],
       [35, 36, 37, 38, 39, 40, 41],
       [42, 43, 44, 45, 46, 47, 48]])
>>> old_main_diagonal = a.diagonal().copy()
>>> np.fill_diagonal(a, np.flipud(a).diagonal())
>>> np.fill_diagonal(np.flipud(a), old_main_diagonal)
>>> a
array([[42,  1,  2,  3,  4,  5, 48],
       [ 7, 36,  9, 10, 11, 40, 13],
       [14, 15, 30, 17, 32, 19, 20],
       [21, 22, 23, 24, 25, 26, 27],
       [28, 29, 16, 31, 18, 33, 34],
       [35,  8, 37, 38, 39, 12, 41],
       [ 0, 43, 44, 45, 46, 47,  6]])

>>> a = np.arange(49).reshape(7, -1)
>>> a
array([[ 0,  1,  2,  3,  4,  5,  6],
       [ 7,  8,  9, 10, 11, 12, 13],
       [14, 15, 16, 17, 18, 19, 20],
       [21, 22, 23, 24, 25, 26, 27],
       [28, 29, 30, 31, 32, 33, 34],
       [35, 36, 37, 38, 39, 40, 41],
       [42, 43, 44, 45, 46, 47, 48]])
>>> old_main_diag_in_reverse = a.diagonal()[::-1].copy()
>>> np.fill_diagonal(a, np.fliplr(a).diagonal())
>>> np.fill_diagonal(np.flipud(a), old_main_diag_in_reverse)
>>> a
array([[ 6,  1,  2,  3,  4,  5,  0],
       [ 7, 12,  9, 10, 11,  8, 13],
       [14, 15, 18, 17, 16, 19, 20],
       [21, 22, 23, 24, 25, 26, 27],
       [28, 29, 32, 31, 30, 33, 34],
       [35, 40, 37, 38, 39, 36, 41],
       [48, 43, 44, 45, 46, 47, 42]])