В списке с четными и нечетными числами. отсортировать четные по возр, нечетные - по убыванию

A=[12,13,4,7,18,21,9,56,8,9,17,29,34]
 
B = [i for i in range(1,len(A)) if i%2==0]
B.sort()
print(B)
 
C = [i for i in range(1,len(A)) if not i%2==0]
C.sort(reverse=True)
print(B+C)

a = [12, 13, 4, 7, 18, 21, 9, 56, 8, 9, 17, 29, 34]
a[::2] = sorted(a[::2])
a[1::2] = sorted(a[1::2], reverse=True)
print(a)

from itertools import zip_longest
a = [12, 13, 4, 7, 18, 21, 9, 56, 8, 9, 17, 29, 34]
a = [j for i in zip_longest(sorted(a[::2]), sorted(a[1::2], reverse=True)) for j in i if j is not None]
print(a)

def main_sort(index):
    for i in range(len(A)):
        if (not A[i]% 2 and not index %2) and A[index] < A[i]:
            A[index], A[i] =  A[i], A[index]
        elif  (A[i]% 2 and index %2) and A[index] > A[i]:
            A[index], A[i] =  A[i], A[index]
        
    
A = [12,13,4,7,18,21,9,56,8,9,17,29,34]
for index in range(len(A)):
        main_sort(index)
 
print(A)

a = [12, 13, 4, 7, 18, 21, 9, 56, 8, 9, 17, 29, 34]
a[::2] = sorted(a[::2])
a[1::2] = sorted(a[1::2], reverse=True)
print(a)
 
from itertools import zip_longest
a = [12, 13, 4, 7, 18, 21, 9, 56, 8, 9, 17, 29, 34]
a = [j for i in zip_longest(sorted(a[::2]), sorted(a[1::2], reverse=True)) for j in i if j is not None]
print(a)