Sort object list by one or multiple attributes in normal or reverse order in python3

sort.py

from operator import attrgetter

def sort_by_attr(alist, *args):
    """
    Sort an object list by one or more of its atributes

    Parameters:
        alist (list): object list
        *args (strings): the name of one or more of the objects attributes
            possibly preceded by a '-' sign to use reversed order 

    Example:
        sort_by(user_list, "name", "-age")
    """

    for fname in reversed(args):

        # Remove order modifier from field name
        reverse = (fname[0] == '-')
        fname   = fname[1:] if fname[0] in ("+", "-") else fname

        # Sort by field name in selected order
        alist.sort(key=attrgetter(fname), reverse=reverse)

        
# An example
#############
class User(object):

    def __init__(self, name, age):
        self.name = name
        self.age  = age

    def __repr__(self):
        return "<User {} {}>".format(self.name, self.age)


users = [User('john', 44), User('lisa', 22), User('anna', 22), User('peter', 77)]


sort_by_attr(users, "name")
print("name:\t", users)
sort_by_attr(users, "-name")
print("-name:\t", users)
sort_by_attr(users, "age")
print("age:\t", users)
sort_by_attr(users, "-age")
print("-age:\t", users)
sort_by_attr(users, "name", "age")
print("name age:\t", users)
sort_by_attr(users, "age", "name")
print("age name:\t", users)
sort_by_attr(users, "age", "-name")
print("age -name:\t", users)
sort_by_attr(users, "-age", "name")
print("-age name:\t", users)