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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 _build_egg(egg, archive_filename, to_dir):
 """Build Setuptools egg."""

    with archive_context(archive_filename):
        # building an egg
        log.warn('Building a Setuptools egg in %s', to_dir)
        _python_cmd('setup.py', '-q', 'bdist_egg', '--dist-dir', to_dir)
    # returning the result
    log.warn(egg)
    if not os.path.exists(egg):
        raise IOError('Could not build the egg.')