import re


def get_words_from_file(filepath):
    """Return the set of all words at least three letters
    long from within a named file.
    """
    with open(filepath) as f:
        #
        # re.findall returns a list of all instances matching a pattern
        # The pattern \w{3,} matches a word at least three letters long
        # f.read() reads the entire contents of a file into a string
        # set() returns a unique set of the values in an iterator
        #
        # So we have:
        #   A unique set of
        #     All words at least three letters long within
        #       The contents of the file f
        #
        return set(re.findall(r"\w{3,}", f.read()))