read from one file and write to another file line by line until end of file

def read_write(read_filename, write_filename):
    file_to_read = open(read_filename, "r")
    file_to_write = open(write_filename, "a")
    for row in file_to_read.readlines():
        file_to_write.write(row)
    file_to_read.close()
    file_to_write.close()