The codon translator

You will write three functions that find the start of a gene, translate an mRNA and say what a change of one base does. The table of the genetic code is made for you at the top of the program, and the amino acids are written with one letter, M for methionine and so on.

The idea. A ribosome starts at the first AUG, reads three bases at a time and stops at a stop codon, which is * in the table.

Your tasks.

1. Finish translate. It gives the amino acids, as a string, from the first AUG to the stop codon. The stop codon is not included. If there is no AUG, it gives an empty string.
2. Finish classify. It compares an old codon and a new codon, and gives "silent", "missense" or "nonsense".
3. Finish changes. It counts how many of the 9 changes of one base in a codon are silent, missense and nonsense, and gives them as a dictionary.