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From: Terry Reedy <tjreedy@udel.edu>
Newsgroups: comp.lang.python
Subject: Re: Undefined behaviour in C [was Re: The Cost of Dynamism]
Date: Sat, 26 Mar 2016 16:44:41 -0400
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Xref: csiph.com comp.lang.python:105783

On 3/26/2016 1:43 PM, Rustom Mody wrote:

> There is this nice piece of OO called the exception hierarchy:

 > https://docs.python.org/2/library/exceptions.html#exception-hierarchy

https://docs.python.org/3/library/exceptions.html#exception-hierarchy

> BaseException =E2=8A=87 Exception =E2=8A=87 EnvironmentError =E2=8A=87 =
IOError

BaseException =E2=8A=87 Exception =E2=8A=87 =E2=8A=87 OSError

> At this point it would have been completely natural for IOError to cont=
inue
> subclassing to all the typical errors
> - File not found
> - No Space left on device

Which is why we now have

       +-- OSError
       |    +-- BlockingIOError
       |    +-- ChildProcessError
       |    +-- ConnectionError
       |    |    +-- BrokenPipeError
       |    |    +-- ConnectionAbortedError
       |    |    +-- ConnectionRefusedError
       |    |    +-- ConnectionResetError
       |    +-- FileExistsError
       |    +-- FileNotFoundError
       |    +-- InterruptedError
       |    +-- IsADirectoryError
       |    +-- NotADirectoryError
       |    +-- PermissionError
       |    +-- ProcessLookupError
       |    +-- TimeoutError

'no space' is MemoryError, but that is a hardward, not OS matter.

> But instead we have an integer errno and we must inquire what that is t=
o
> figure out what the exact IOError was

This statement is obsolete, but explains why the above was added in 3.3.

--=20
Terry Jan Reedy