def filter_dict(my_dict, number):
    """
    Filters all entries in my_dict with values less than or
    equal to number
    """
    for key in my_dict.keys():
        if my_dict[key] <= number:
            del my_dict[key]


my_dict.keys() returns a new list of the keys and avoids the problem of
trying to iterate of a dictionary that we are modifying.