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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 unique_file_name(base_name, extension=''):
    '''
    Creates a unique file name based on the specified base name.

    @base_name - The base name to use for the unique file name.
    @extension - The file extension to use for the unique file name.

    Returns a unique file string.
    '''
    idcount = 0

    if extension and not extension.startswith('.'):
        extension = '.%s' % extension

    fname = base_name + extension

    while os.path.exists(fname):
        fname = "%s-%d%s" % (base_name, idcount, extension)
        idcount += 1

    return fname