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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 avail_sizes(call=None):
    '''
    Return a dict of all available VM sizes on the cloud provider with
    relevant data.
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The avail_sizes function must be called with '
            '-f or --function, or with the --list-sizes option'
        )

    conn = get_conn()

    sizes = conn.fixed_server_flavors()

    return sizes