Enable reading from a tar file

[pwrose]

AlphaFold db bundles files as tar files.

Rather than un-taring the files and then parsing the cif.gz files, specific files could be read directly from the tar file, e,g.,

filename = "AF-O52908-F1-model_v2.cif.gz"

with tarfile.open("UP000000799_192222_CAMJE_v2.tar") as tf:
    with gzip.open(tf.extractfile(filename), mode="rt") as gf:
        gf.readlines()

With some modifications to CifReader, it should be possible to do this:

with tarfile.open("UP000000799_192222_CAMJE_v2.tar") as tf:
    cfr = CifFileReader()
    file_obj = tf.extractfile(filename)
    cif_obj = cfr.read(file_obj, output='cif_dictionary')