[Python-Dev] When to use EOFError? (original) (raw)

André Malo nd at perlig.de
Wed Jun 22 12:22:49 EDT 2016

There is a design question. If you read file in some format or with some protocol, and the data is ended unexpectedly, when to use general EOFError exception and when to use format/protocol specific exception?

For example when load truncated pickle data, an unpickler can raise EOFError, UnpicklingError, ValueError or AttributeError. It is possible to avoid ValueError or AttributeError, but what exception should be raised instead, EOFError or UnpicklingError? Maybe convert all EOFError to UnpicklingError? Or all UnpicklingError caused by unexpectedly ended input to EOFError? Or raise EOFError if the input is ended after completed opcode, and UnpicklingError if it contains truncated opcode?

I often concatenate multiple pickles into one file. When reading them, it works like this:

try: while True: yield pickle.load(fp) except EOFError: pass

In this case the truncation is not really unexpected. Maybe it should distinguish between truncated-in-the-middle and truncated-because-empty.

(Same goes for marshal)

Cheers,

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