> On Nov 1, 2017, at 21:13, Chris Lattner via swift-evolution > <swift-evolution@swift.org> wrote: > >> On Nov 1, 2017, at 3:20 AM, Richard Wei <rxr...@gmail.com >> <mailto:rxr...@gmail.com>> wrote: >>>> >>>> Since you bring it up, Python exceptions will be annoying - As with other >>>> languages, Python can throw from an arbitrary expression. Modeling >>>> everything as throws in Swift would be super-annoying and unergonomic for >>>> the programmer, because we'd require 'try' everywhere. Thoughts on what >>>> to do about that are welcome! >>> >>> Requiring ‘try’ on every statement is annoying, but not having the ability >>> to catch python exceptions is annoying too. We could probably make python >>> exception handling an opt-in feature. For example: >>> >>> try Python.do { >>> let a = np.array([1, 2, 3]) >>> let b = np.array([[2], [4]]) >>> print(a.dot(b)) // matrix mul with incompatible shapes >>> } >>> catch let error as PythonException { >>> // Handle PythonError.valueError(“objects are not aligned”) >>> } >> >> To correct my example: >> >> do { >> try Python.do { >> let a = np.array([1, 2, 3]) >> let b = np.array([[2], [4]]) >> print(a.dot(b)) // matrix mul with incompatible shapes >> } >> } >> catch let error as PythonException { >> // Handle PythonError.valueError(“objects are not aligned”) >> } >> >> Maybe ‘Python.do {}’ should be called something like ‘Python.safely {}’. > > That’s a super interesting way to model this. I’ll need to ponder on it > more, but it is certainly a nice ergonomic solution. > > Question though: how does it work? Say the first np.array call threw a > python exception: > >> try Python.do { >> let a = np.array([1, 2, 3]) >> let b = np.array([[2], [4]]) >> print(a.dot(b)) // matrix mul with incompatible shapes >> } > > > We can definitely make the python glue code notice it, catch it and squirrel > it away somewhere, but without compiler hacks we couldn’t make it jump out of > the closure. This means that np.array would have to return something, and > the calls below it would still execute, or am I missing something?
We make PythonObjects internally nullable (only in the exception-caught state). The second np.array would just return a null PythonObject. To be specific, we define three states in the python overlay: - Normal state: PythonObjects are guaranteed to be non-null. Any exception traps. - Exception-catching state: PythonObjects are still guaranteed to be non-null. Any exception triggers the exception-caught state. - Exception-caught state: PythonObjects are nullable — all python expressions return a null PythonObject. The exception-catching state is entered during the execution of Python.do’s body. -Richard > > -Chris > > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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