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Solve the following problem using Python, implementing the functions described below, one line at a time
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<USER_TASK:>
Description:
 def change_password(username, new_password):
 """ Change password for given `username`. Args: username (str):
 User's name. new_password (str):
 User's new password. """

    assert username in passwd_reader.load_users(),\
           "Username '%s' not found!" % username

    sh.ftpasswd(
        "--change-password",
        passwd=True,        # passwd file, not group file
        name=username,
        stdin=True,         # tell ftpasswd to read password from stdin
        file=settings.LOGIN_FILE,
        _in=new_password
    )

    reload_configuration()