For args= ['', '0', 'P1', 'with', '10'] and students=[['1', '2', '3', 6]] it prints:
[[['1', '2', '3', 6]]]
[[['10', '2', '3', 6]]]
The expected output was :
[[['1', '2', '3', 6]]]
[[['1', '2', '3', 6]]]
But it somehow changes the backup_list any quick solutions?
backup_list.append(students[:])
print(backup_list)
students[int(args[1])][0] = args[4]
print(backup_list)
[:] make a shallow copy. You need a deep copy:
import copy
backup_list.append(copy.deepcopy(students))
Full program:
import copy
backup_list = []
args= ['', '0', 'P1', 'with', '10']
students=[['1', '2', '3', 6]]
backup_list.append(copy.deepcopy(students))
print(backup_list)
students[int(args[1])][0] = args[4]
print(backup_list)
Output:
[[['1', '2', '3', 6]]]
[[['1', '2', '3', 6]]]
The documentation explains the difference between shallow and deep copy:
A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.
A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.
