the index (between the [ ]) had three parts:
first number stands for the startindex, here it is 7, which corresponds to test[7]=49.
second number stands for end index, it is test[5]=25.
third number is the stepsize of the range: -1 means reversed. So test[7:5:-1] = [49,36].
remark: Python works with zero based indexing.
remark: the end index is never included.
