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POI want to return a value AND raise an exception, does this mean I'm doing something wrong?
 

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  1. POI want to return a value AND raise an exception, does this mean I'm doing something wrong?
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    <p>I have a number of functions that parse data from files, usually returning a list of results.</p> <p>If I encounter a dodgy line in the file, I want to soldier on and process the valid lines, and return them. But I also want to report the error to the calling function. The reason I want to report it is so that the calling function can notify the user that the file needs looking at. I don't want to start doing GUI things in the parse function, as that seems to be a big violation of separation of concerns. The parse function does not have access to the console I'm writing error messages to anyway.</p> <p>This leaves me wanting to return the successful data, but also raise an exception because of the error, which clearly I can't do.</p> <p>Consider this code:</p> <pre><code>try: parseResult = parse(myFile) except MyErrorClass, e: HandleErrorsSomehow(str(e)) def parse(file): #file is a list of lines from an actual file err = False result = [] for lines in file: processedLine = Process(line) if not processedLine: err = True else result.append(processedLine) return result if err: raise MyErrorClass("Something went wrong") </code></pre> <p>Obviously the last three lines make no sense, but I can't figure out a nice way to do this. I guess I could do <code>return (err, result)</code>, and call it like</p> <pre><code>parseErr, parseResult = parse(file) if parseErr: HandleErrorsSomehow() </code></pre> <p>But returning error codes seems un-pythonic enough, let alone returning tuples of error codes and actual result values.</p> <p>The fact that I feel like I want to do something so strange in an application that shouldn't really be terribly complicated, is making me think I'm probably doing something wrong. Is there a better solution to this problem? Or is there some way that I can use <code>finally</code> to return a value and raise an exception at the same time?</p>
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    1. USCam Jackson
    1. USCam Jackson
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    1. COIn this case, I would probably return a tuple `processedData,errorInformation`, with `errorInformation` being an empty string if no error occurred. Another option would be to use a callback function, called with some error information if an error occurs - if the caller doesn't care, it could pass `None` as the callback.
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      1. USRussell Borogove
 

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