def logReSubn(subnExpr, preComment, postComment, errorMsg='') -> str:
    """
    Takes in the result of a re.subn call, subnExpr, and
    logs preComment to stdout, then logs postComment and specifies the
    number of subs.
    Prints errorMsg in case of 0 subs.

    Returns the string from subnExpr with replacements made.
    """
    out = subnExpr[0]
    subs = subnExpr[1]
    print(preComment)
    print(str(subs) + ' ' + postComment)
    if (subs == 0 and errorMsg != ''):
        print(errorMsg)
    return out