sys.stdout.detach() results in ValueError

Terry Reedy tjreedy at
Thu Mar 8 01:10:25 CET 2012

On 3/7/2012 5:35 PM, Peter Kleiweg wrote:
> Dave Angel schreef op de 7e dag van de lentemaand van het jaar 2012:
>> On 03/07/2012 02:41 PM, Peter Kleiweg wrote:
>>> I want to write out some binary data to stdout in Python3. I
>>> thought the way to do this was to call detach on sys.stdout. But
>>> apparently, you can't. Here is a minimal script:
>>>       #!/usr/bin/env python3.1
>>>       import sys
>>>       fp = sys.stdout.detach()
>>> Not yet using fp in any way, this script gives the following error:
>>>       Exception ValueError: 'underlying buffer has been detached' in
>>> Same in Python 3.1.4 and Python 3.2.2
>>> So, what do I do if I want to send binary data to stdout?
>> sys.stdout.write(  some_binary_data )
> TypeError: must be str, not bytes

Right, you can only send binary data to file opened in binary mode. The 
default sys.stdout is in text mode. I am pretty sure that remains true 
even if stdout is redirected. (You did not mention your OS.) You would 
have to open such a file and make sys.stdout point to it.
sys.stdout = my_binary_file.
But why do that? Just open the file and write to it directly without the 

Terry Jan Reedy

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