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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 walnut_data():
 """Tomographic X-ray data of a walnut. Notes ----- See the article `Tomographic X-ray data of a walnut`_ for further information. See Also -------- walnut_geometry References .. _Tomographic X-ray data of a walnut: https://arxiv.org/abs/1502.04064 """

    # TODO: Store data in some ODL controlled url
    url = 'http://www.fips.fi/dataset/CT_walnut_v1/FullSizeSinograms.mat'
    dct = get_data('walnut.mat', subset=DATA_SUBSET, url=url)

    # Change axes to match ODL definitions
    data = np.swapaxes(dct['sinogram1200'], 0, 1)[::-1, ::-1]
    data = data.astype('float')

    # Very crude gain normalization
    data = -np.log(data / np.max(data, axis=1)[:, None])
    return data