sys.stdout.detach() results in ValueError

Terry Reedy tjreedy at udel.edu
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 
above.

-- 
Terry Jan Reedy




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