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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_file_extension(format_):
 """Format identifier -> file extension"""

    if format_ not in FORMAT_IDENTIFIER_TO_FORMAT_CLASS:
        raise UnknownFormatIdentifierError(format_)

    for ext, f in FILE_EXTENSION_TO_FORMAT_IDENTIFIER.items():
        if f == format_:
            return ext

    raise RuntimeError("No file extension for format %r" % format_)