word_count.py

#!/usr/bin/env python


def read_stdin() -> list:
    """
    Returns a list of str read from stdin.
    Use whitespaces as word separator.
    """
    # 0 is the file descriptor of stdin.
    # A more clever way would have been to use sys.stdin, but it is forbidden for pedagogic reasons
    with open(0) as stdin:
        # Cannot use readline because stdin is stored in live memory and is forgotten once it is read.
        # So if you use readline against it, you will read only the first line
        return stdin.read().split()


def count_word_number(words: list) -> dict:
    """
    Compute number of word occurrence in a list.
    Returns a dict with a word as key and its occurrence number as value
    """
    count = {}
    for word in words:
        if word in count:
            count[word] += 1
        else:
            count[word] = 1
    return count


def repr_ordered_word_count(word_count: dict) -> str:
    """
    Build a string with a word and its occurrence number per line
    Lines are ordered by descending occurrence number
    """
    return "\n".join(
        f"{occurrence_nbr} {word}"
        for word, occurrence_nbr in sorted(word_count.items(), key=lambda key_value: key_value[1], reverse=True)
    )


def main():
    print(repr_ordered_word_count(count_word_number(read_stdin())))


def test():
    assert count_word_number(["foo", "bar", "foo", "eggs", "bar", "", "bar"]) == {"foo": 2, "bar": 3, "eggs": 1, "": 1}
    assert repr_ordered_word_count({"foo": 1, "bar": 3}) == "3 bar\n1 foo"


if __name__ == "__main__":
    main()