Embedded Python And raw_input

If you ever messed with embedded Python you would know that you can’t use the Win32 Console so easily. For that you will have to hack around a few bits in order to bind the stdin and stdout with the Win32 ones. Another familiar technique is to override sys.stdout with your own class that implements the ‘write’  method. So every time something goes to output this method is really called with an argument which is then being printed on the screen with whatever Win32 API you want, to name WriteFile

This same technique works also for stderr which is used when one writes some invalid text which doesn’t compile and an exception is thrown.

‘Hooking’ both stdout and stderr we still got stdin out of the loop. Now all these years that embedded Python was around I have never encountered the problem that the stdin doesn’t work with raw_input(). Don’t be confused, the way things work in embedded Python, it doesn’t mean that the interactive interpreter is fed from stdin, it’s a bit more messy. In all examples of embedded Python you have to implement your own interactive interpreter on your own, therefore you bypass stdin from the first moment. Hence if you never used raw_input you will not know if it’s broken or not. So I want to thank a special friend for reporting this bug to me… 😉 J

The fix… To fix the problem I tried to replace sys.stdin with my own implementation of a class with a ‘read’ method (by guessing-because ‘write’ is stdout’s). Doing so I found out that the method name should be ‘readline’ according to raw_input’s shouts at me. Then I renamed the method and the implementation was to call a function that I wrote in C and which is wrapped in Python that reads input from the console (Using ReadFile(GetStdHandle(STD_INPUT_HANDLE),…) and returns that input string rawly. That did the trick and now raw_input works again.

I am pretty sure that all embedded Python users out there will need this hack if they already hack stdout…

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