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

Ronald Oussoren ronaldoussoren at mac.com
Tue Jan 17 12:25:18 CET 2012

On 17 Jan, 2012, at 11:59, anatoly techtonik wrote:
> If you track this more closely, you'll notice there are four issues (surprises) from the user point of view:
> 1. print() buffers output on Python3
> 2. print() also buffers output on Python2, but only on Linux
> 3. there is some useless '-u' command line parameter
>     (useless, because the last thing user wants is not only care about Python 2/3, but also how to invoke them)
> 4. print() is not guilty - it is sys.stdout.write() that buffers output
> 1-2 discussion was about idea to make new print() function behavior more 'pythonic', i.e. 'user-friendly' or just KISS, which resulted in adding a flush parameter
> 3 is a just a side FYI remark
> 4 doesn't relate to python-ideas anymore about fixing print() - it is about the *cause* of the problem with print() UX, which is underlying sys.stdout.write() behavior
> I asked 4 here, because it is the more appropriate place not only to ask if it can be/will be fixed, but also why. The target audience of the question are developers.

All four "issues" are related to output buffering and how that is not user-friendly. The new issue you raise is the same as before: sys.stdout is line buffered when writing to a tty, which means that you have to explictly flush output when you want to output a partial line.  Why is this a problem for you? Is that something that bothers you personally or do you have data that suggests that this is a problem for a significant amount of (new) users?


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