New submission from Robert Collins:
The io library rejects unbuffered text I/O, but this is not documented - and in
fact can be manually worked around:
binstdout = io.open(sys.stdout.fileno(), 'wt', 0)
sys.stdout = io.TextIOWrapper(binstdout, encoding=sys.stdout.encoding)
will get a sys.stdout that is unbuffered.
Note that writing to a pipe doesn't really need to care about buffering anyway,
if the user writes 300 characters, the codec will output a single block and the
IO made will be one write:
This test script:
import sys
import io
stream = io.TextIOWrapper(io.open(sys.stdout.fileno(), 'wb', 0),
encoding='utf8')
for r in range(10):
stream.write(u'\u1234'*500)
When run under strace -c does exactly 10 writes: so the performance is
predictable. IMO it doesn't make sense to prohibit unbuffered text write I/O.
readers may be another matter, but that doesn't suffer the same latency issues.
----------
messages: 184025
nosy: rbcollins
priority: normal
severity: normal
status: open
title: ValueError: can't have unbuffered text I/O for io.open(1, 'wt', 0)
type: behavior
versions: Python 2.6, Python 2.7, Python 3.1, Python 3.2, Python 3.3, Python
3.4, Python 3.5
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Python tracker <[email protected]>
<http://bugs.python.org/issue17404>
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