Setting sys.stdin to an invalid input stream under interactive mode causes interpreter run loop forever:

Python 3.3a0 (default:22ae2b002865+, Mar 30 2011, 21:17:03) 
[GCC 4.4.4] on linux2
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>>> import sys
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>>> sys.stdin = None
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Not only setting to None but also to any other invalid input stream could cause this. It's because in the beginning of PyRun_InteractiveOneFlags(), in order to get stdin encoding, the code tries to get sys.stdin and check if it's valid(not NULL, not None, has "encoding" attribute), if not, return -1 directly, then the loop in PyRun_InteractLoopFlags() continues and does the same thing. I think this should be fixed by using the Py_FileSystemDefaultEncoding instead when sys.stdin is invalid.