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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 load_from_file(filename):
    '''
    Load a topology from filename and return it.
    '''
    t = None
    with open(filename, 'rU') as infile:
        tdata = infile.read()
        t = Topology.unserialize(tdata)
    return t