#4617: Previously it was illegal to delete a name from the local namespace if it occurs as a free variable in a nested block. This limitation of the compiler has been lifted, and a new opcode introduced (DELETE_DEREF). This sample was valid in 2.6, but fails to compile in 3.x without this change:: >>> def f(): ... def print_error(): ... print(e) ... try: ... something ... except Exception as e: ... print_error() ... # implicit "del e" here This sample has always been invalid in Python, and now works:: >>> def outer(x): ... def inner(): ... return x ... inner() ... del x There is no need to bump the PYC magic number: the new opcode is used for code that did not compile before.