Correct behavior for failure during __init__()

[Aahz Maruch]

In article <mailman.990053304.18687.python-list at python.org>,
Jeff Putsch  <putsch at fiber.mxim.com> wrote:
>
>I'm wrapping a C library with with python and swig. I'm defining a class
>like this (wLib) is the wrapped C library:
>
>   import wLib
>
>   class ddId:
>       def __init__(self, arg1, arg2):
>           t1 = wLib.createObj(arg1, arg2)
>           if t1:
>               self.Id = t1
>           else:
>               NOW WHAT?
>
>It is possible that the call to wLib.createObj does not succeed. In this
>case it is not clear to me what I should do where I've marked "NOW WHAT?"
>in the code above.

Generally, the answer is to raise an exception (presuming this situation
means that an error has occurred that makes the new instance unusable).
For example, the open() function returns a file object; if open() fails,
it raises an exception (usually an IOError):

>>> open('foo')
Traceback (innermost last):
  File "<stdin>", line 1, in ?
IOError: [Errno 2] No such file or directory: 'foo'
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