class File:
    def __init__(self, filename):
        self.filename = filename

    def open(self): ...
    def read(self):  ...
    def write(self): ...
    def close(self): ...
# end of class File

class Socket:
    def __init__(self, address, port):
        self.address = address
        self.port = port

    def open(self): ...
    def read(self): ...
    def write(self): ...
    def close(self): ...
# end of class Socket

# read_data works equally well with both File and Socket
def read_data(source):
    data = source.read()
    source.close()
    return data