AttributeError in Popen.communicate()

BPO	30203

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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assignee = None
closed_at = None
created_at = <Date 2017-04-29.08:21:08.187>
labels = ['type-bug']
title = 'AttributeError in Popen.communicate()'
updated_at = <Date 2017-04-29.08:24:46.146>
user = 'https://bugs.python.org/LukeCampagnola'

bugs.python.org fields:

activity = <Date 2017-04-29.08:24:46.146>
actor = 'Luke Campagnola'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2017-04-29.08:21:08.187>
creator = 'Luke Campagnola'
dependencies = []
files = []
hgrepos = []
issue_num = 30203
keywords = []
message_count = 2.0
messages = ['292575', '292577']
nosy_count = 1.0
nosy_names = ['Luke Campagnola']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue30203'
versions = ['Python 3.5']

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In my application, calling communicate() on a Popen instance is giving the following exception:

. . .
File "/usr/lib/python3.5/subprocess.py", line 1072, in communicate
stdout, stderr = self._communicate(input, endtime, timeout)
File "/usr/lib/python3.5/subprocess.py", line 1693, in _communicate
stdout = self._fileobj2output[self.stdout]
AttributeError: 'Popen' object has no attribute '_fileobj2output'

I have not been able to reproduce this in a simple example, but I imagine this could happen if Popen._communicate() raises an exception in the first 20 lines or so--this would cause _communication_started to be set True, even though _fileobj2output has not been initialized.

I suggest setting self._fileobj2output = None in Popen.__init__() and changing the relevant code in _communicate() from

            if not self._communication_started:
                self._fileobj2output = {}

to:

            if self._fileobj2output is None:
                self._fileobj2output = {}

Update: this appears to be the prior exception that causes _communication_started and _fileobj2ouput to be out of sync:

File "/usr/lib/python3.5/subprocess.py", line 1072, in communicate
stdout, stderr = self._communicate(input, endtime, timeout)
File "/usr/lib/python3.5/subprocess.py", line 1672, in _communicate
self.stdin.flush()
ValueError: flush of closed file

I can reproduce with the following code, in version 3.12, which involves closing stdin before first communicate() so that you get the exception in _communicate(), and then try to communicate again when communicate again when _communication_started=True but the fileobj attr was not set because of the exception.

I'm not sure that's a realistic example that needs a fix. If someone can demonstrate that it IS a realistic scenario, the fix would be easy, along the lines OP suggested.

from subprocess import Popen, PIPE

p=Popen('ls', stdin=PIPE, stdout=PIPE)
p.stdin.close()
try:
    p.communicate()
except:
    pass
p.communicate()


Traceback (most recent call last):
  File "/Users/ak/opensource/cpython4/a.py", line 25, in <module>
    p.communicate()
  File "/Users/ak/opensource/cpython4/Lib/subprocess.py", line 1208, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ak/opensource/cpython4/Lib/subprocess.py", line 2035, in _communicate
    stdout = self._fileobj2output[self.stdout]
             ^^^^^^^^^^^^^^^^^^^^
AttributeError: 'Popen' object has no attribute '_fileobj2output'

Encountered this issue, any idea?

result = subprocess.Popen(f"{self.windows_wechat_start_path} {self.dll_path} {self.port}", shell=True,
                                  stdout=subprocess.PIPE, stderr=subprocess.PIPE, encoding='utf-8')
result = ''.join(result.communicate())
logger.debug(result)

  File "C:\Users\Henry\Desktop\XYBot\pywxdll\pywxdll.py", line 54, in windows_start_wechat_and_inject
    result = ''.join(result.communicate())
AttributeError: 'CompletedProcess' object has no attribute 'communicate'

@HenryXiaoYang

AttributeError: 'CompletedProcess' object has no attribute 'communicate'

@HenryXiaoYang your issue looks different and doesn't match what your code snippets say. result would only be of CompletedProcess type if you had assigned it to a result = subprocess.run(...), not = subprocess.Popen(...) which would be the instance you can call communicate() on.

pythongh-70560: pythongh-74389: subprocess.Popen.communicate() now ig…

gh-74389: gh-70560: subprocess.Popen.communicate() now ignores stdin.…

pythongh-74389: pythongh-70560: subprocess.Popen.communicate() now ig…

[3.14] gh-74389: gh-70560: subprocess.Popen.communicate() now ignores…

[3.13] gh-74389: gh-70560: subprocess.Popen.communicate() now ignores…

Fix memoryview and closed stdin handling in _communicate_streams_posix

Factor out _flush_stdin() and _make_input_view() helpers

pythongh-74389: pythongh-70560: subprocess.Popen.communicate() now ig…

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AttributeError in Popen.communicate() #74389

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AttributeError in Popen.communicate() #74389

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LukeCampagnola commented on Apr 29, 2017

LukeCampagnola commented on Apr 29, 2017

akulakov commented on Oct 10, 2022

HenryXiaoYang commented on Jul 7, 2024

gpshead commented on Nov 29, 2025

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