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davidfor - I still think in C and asm

The conversion could chew cycles, IIRC conversions in .Net CIL and JRE were/are known to be slow, dunno about Python IL.
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LDMartin1959 - I import books into a 'receiving dock' library and do an inter library Find Duplicates. Any duplicates get moved into a 'duplicates' library, and the non-duplicates get moved to the 'main' library. For me this works better functionally and it's faster than doing everything in one library - and it keeps my 'main' library pristine.
BR