I start to look at whether some subset of functions or classes are not referenced by other subsets of functions or classes in a module when it gets to about 1K LoC, and if I don't find any by the time it gets to about 1500 LoC, I start to look at ways I can refactor the code in the module to be less coupled. This might just be anecdotal, but in all the python libraries I've looked at (including the larger 30K+ LoC ones) the quality of code in a module tends to be lower if the module is over around 1500 LoC.
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