from collections import defaultdict

my_list = [21, 4, 37, 46, 7, 56, 7, 69, 2, 86, 1]

print("The list is :")
print(my_list)

my_key = 46
print("The key is ")
print(my_key)

my_sum = 0
my_result = []

for ele in my_list:
   if ele != my_key:
      my_sum += ele

   else:
      my_result.append(my_sum)
      my_result.append(ele)
      my_sum = 0

my_result.append(my_sum)

print("The resultant list is :")
print(my_result)

The list is :
[21, 4, 37, 46, 7, 56, 7, 69, 2, 86, 1]
The key is
46
The resultant list is :
[62, 46, 228]