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[Python-Dev] When to use EOFError?

Random832 random832 at fastmail.com
Wed Jun 22 10:31:27 EDT 2016 
On Tue, Jun 21, 2016, at 16:48, Serhiy Storchaka wrote:
> 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?

I think this is the most appropriate. If the calling code needs to know
the original reason it can find it in __cause__.

My instinct, though, (and I'm aware that others may not agree, but I
thought it was worth bringing up) is that loads should actually always
raise a ValueError, i.e. my mental model of loads is like:

def loads(s):
   f = BytesIO(s)
   try:
      return load(f)
   except UnpicklingError as e:
      raise ValueError from e
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