[Python-Dev] Backwards incompatible sys.stdout.write() behavior in Python 3 (Was: [Python-ideas] Pythonic buffering in Py3 print()) (original) (raw)

Guido van Rossum guido at python.org
Fri Jan 13 16:49:56 CET 2012

I think this may be because in Python 2, there is a coupling between stdin and stderr (in the C stdlib code) that flushes stdout when you read stdin. This doesn't seem to be required by the C std, but most implementations seem to do it. http://stackoverflow.com/questions/2123528/does-reading-from-stdin-flush-stdout

I think it was a nice feature but I can see problems with it; apps that want this behavior ought to bite the bullet and flush stdout.

On Fri, Jan 13, 2012 at 7:34 AM, anatoly techtonik <techtonik at gmail.com>wrote:

Posting to python-dev as it is no more relates to the idea of improving print().

sys.stdout.write() in Python 3 causes backwards incompatible behavior that breaks recipe for unbuffered character reading from stdin on Linux - http://code.activestate.com/recipes/134892/ At first I though that the problem is in the new print() function, but it appeared that the culprit is sys.stdout.write() Attached is a test script which is a stripped down version of the recipe above. If executed with Python 2, you can see the prompt to press a key (even though output on Linux is buffered in Python 2). With Python 3, there is not prompt until you press a key. Is it a bug or intended behavior? What is the cause of this break? -- anatoly t.

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