The first square brackets contain a list of values to be returned. The second square brackets contain an expression whose calculation results in a slice for the first list. bin_str. count ("1")%2 means that we calculate the number of occurrences of' 1 ' in bin_str and check whether the number of units is even. (parity = = "even") will give 1 or 0 depending on whether an even number of units is expected or an odd one. in essence, it looks something like this:

imagine that bin_str is equal to '010101' and parity is equal to 'even'
[0, 1][bin_str.count("1") % 2 == (parity == "even")] = [0, 1][3 % 2 == (parity == "even")] = [0, 1][3 % 2 == (1)] = [0, 1][1 == (1)] = [0, 1][1] = 1
Here it is necessary to understand that when comparing (==) two operands, it turns out True if they are equal and False if they are not equal. True is the same as 1 False is the same as 0. True = 1, False = 0. True+True = 2, False + False = 0, ... I hope it helped somehow, if something is wrong experienced wars will correct.