====== Solution to Exercise 3 (Day 1, morning session) ======

One of the entries in ''not_working.data'' (number 8 in the second line) contains an additional special character, and Python fails to convert it to an integer using the ''int'' function (line 31 in ''convert_to_dict.py''). Python correctly raises an exception, but it is captured in the ''try ... except'' statement to ''get_number_dict''.

This kind of bug is quite common, and is due to forgetting to handle incorrect input in a function. There are two possible approaches to solving the bug: The first is to detect when the input cannot be converted to integer (e.g., by catching a ''ValueError'' around line 31); The second is to raise an appropriate exception. In this second case you should make sure to test that the ''walk_string'' function raises the correct exception, but also that ''get_number_dict'' does not stop it from being raised.