[Python-Dev] Why are captured parameters also listed in co_varnames? (original) (raw)

Andrea Griffini agriff at tin.it
Tue Jul 2 11:27:02 CEST 2013


I'm trying to understand how CPython implements closure variable capture and there is one minor point I can't understand.

When a local is captured it gets allocated in co_cellvars and is accessed with (LOAD|STORE)_DEREF, and this is clear. However when a local is coming from a parameter it gets ALSO allocated in co_varnames even if the local slot apparently is not accesible because *_FAST opcodes are not generated.

Is there a technical reason for this? It happens in CPython 2, 3 and even in PyPy...

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