Дана строка S и текстовый файл. Добавить строку S в конец файла.(Питон)

with open('file.txt' , 'a') as f:
    f.write('some string')
#...

def stringer(mstr,my_filename, fext2):
    with open(my_filename + '.' + fext2, 'a', encoding='utf-8')as fp:
        print(mstr, file=fp, sep='\n')
 
 
if __name__ == '__main__':
    my_filename = None
    fex2 = None
    mstr = input()
    stringer(mstr,my_filename='test', fext2='txt')

def stringer(mstr, my_filename, fext2):
    with open(my_filename + '.' + fext2, 'w', encoding='utf-8')as fp:
        print(mstr, file=fp, sep='\n')
 
 
def reader(my_filename, fext2):
    with open(my_filename + '.' + fext2, 'r', encoding='utf-8') as fp:
        data = fp.readlines()
    print(data)
 
 
if __name__ == '__main__':
    my_filename = None
    fext2 = None
    mstr = input()
    stringer(mstr, my_filename='test', fext2='txt')
    reader(my_filename='test', fext2='txt')

with open("output.txt", "a") as out:
    print(s, file=out)

def addf(my_filename, fext2):
    with open(my_filename + '.' + fext2, 'a', encoding='utf-8') as fp:
        print(mstr, file=fp, sep="\n")
 
 
if __name__ == '__main__':
    mstr = input
    my_filename = None
    fex2 = None
    addf(my_filename='test', fext2='txt')