So I was wondering if anybody wants to help me with this. I don't even understand where to begin? Any help would be appreciated.

Write a function called `count_bases` that counts the number of times each letter occurs in a given string. The results should be returned as a dictionary, with letters in upper case as keys and the number of occurrences as (integer) values 

For example when the function is called with the string 'ATGATAGG', it should return `{'A': 3, 'T': 2, 'G': 3, 'C': 0}`. Please ensure your function uses return, not print(). The order of the keys in the dictionary does not need to follow this order (2 marks). 

Make sure that your function works when passed any lower and/or uppercase DNA characters in the sequence string. (2 marks)

DNA sequences sometimes contain letters other than A, C, G to T to indicate degenerate nucleotides. For example, R can represent A or G (the purine bases). If the program encounters any letter other than A, C, G or T, it should also count the frequency of that letter and return within the dictionary object. (2 marks).