len is always a more generic form (applies to all kinds of sequences), and hence preferred. But Table.vector is a numpy array if USE_NUMPY=1 and tuple otherwise. Please check your main Makefile and see if you have set USE_NUMPY=0 (or passing the same in command line).
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Till this is close, replaced table.vector.size with len(table.vector).
len is always a more generic form (applies to all kinds of sequences), and hence preferred. But Table.vector is a numpy array if USE_NUMPY=1 and tuple otherwise. Please check your main Makefile and see if you have set USE_NUMPY=0 (or passing the same in command line).