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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 sr_list(call=None):
    '''
    Geta list of storage repositories

    .. code-block:: bash

        salt-cloud -f sr_list myxen

    '''
    if call != 'function':
        raise SaltCloudSystemExit(
            'This function must be called with -f, --function argument.'
        )
    ret = {}
    session = _get_session()
    srs = session.xenapi.SR.get_all()
    for sr in srs:
        sr_record = session.xenapi.SR.get_record(sr)
        ret[sr_record['name_label']] = sr_record
    return ret