New submission from Frost Ming <[email protected]>:
The following snippet behaves differently between Windows and POSIX.
import subprocess
import time
p = subprocess.Popen("ls -l", shell=True, stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
print(p.stdout.read(1)) # read 1 byte
print(p.communicate()) # Returns empty output
It works fine on Windows and Python 2.x(communicate() returning the remaining
output). So from the best guess it should be the expected behavior.
The reason behind this is that Popen.stdout is a BufferedReader. It stores all
output in the buffer when calling read(). However, communicate() and the lower
API _communicate() use a lower level method os.read() to get the output, which
does not respect the underlying buffer. When an empty output is retrieved the
file object is closed then.
First time to submit a bug report and pardon me if I am getting anything wrong.
----------
components: 2to3 (2.x to 3.x conversion tool), IO, Library (Lib)
messages: 374366
nosy: Frost Ming, brett.cannon, vstinner
priority: normal
severity: normal
status: open
title: BufferedReader causes Popen.communicate losing the remaining output.
versions: Python 3.10, Python 3.7, Python 3.8, Python 3.9
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<https://bugs.python.org/issue41406>
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