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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 spec_fn(spec_dir='.'):
 """ Return the filename for a .spec file in this directory. """

    specs = [f for f in os.listdir(spec_dir)
             if os.path.isfile(f) and f.endswith('.spec')]
    if not specs:
        raise exception.SpecFileNotFound()
    if len(specs) != 1:
        raise exception.MultipleSpecFilesFound()
    return specs[0]