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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_user(prompt=None):
 """ Prompts the user for his login name, defaulting to the USER environment variable. Returns a string containing the username. May throw an exception if EOF is given by the user. :type prompt: str|None :param prompt: The user prompt or the default one if None. :rtype: string :return: A username. """

    # Read username and password.
    try:
        env_user = getpass.getuser()
    except KeyError:
        env_user = ''
    if prompt is None:
        prompt = "Please enter your user name"
    if env_user is None or env_user == '':
        user = input('%s: ' % prompt)
    else:
        user = input('%s [%s]: ' % (prompt, env_user))
        if user == '':
            user = env_user
    return user