[issue25452] Add __bool__() method to subprocess.CompletedProcess

[STINNER Victor]

STINNER Victor added the comment:

For all reasons alread given in the previous comment and my comment below, I 
reject the proposed change.


Serhiy> See also issue26748. Classes usually have True boolean value, but empty 
enum classes were False-y by accident. This was considered a bug.

Another example: issue #13936, "RFE: change bool(datetime.time(0, 0, 0)) to 
evaluate as True". datetime.time was changed in Python 3.5 to always be true, 
especially for the time 00:00:00. It's the opposite of the proposed change for 
CompletedProcess.


The problem is also that different users can expect a different answer from 
bool(CompletedProcess): non-zero return code, non-empty stdout, empty stderr, 
etc.

CompleteProcess is a complex object with many attributes, it's not as simple as 
a tuple or a string, where the truthness is obvious.


> Richard Neumann: "A useless use case is attached."

"if subprocess.run(...):"

Sorry, I'm not convinced that the need of breaking the backward compatibility 
for this "useless use case". It's trivial to split it in two lines:

"cmd = subprocess.run(...); if cmd.returncode: (...)"

By the way, it became common that I write such code, and in this case, I need 
the returncode value in the if block:

"cmd = subprocess.run(...); if cmd.returncode: sys.exit(cmd.returncode)".

So I need the CompletedProcess object anyway.

--
resolution:  -> rejected
stage: needs patch -> resolved
status: open -> closed

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

See also issue26748. Classes usually have True boolean value, but empty enum 
classes were False-y by accident. This was considered a bug.

--

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Raymond Hettinger]

Raymond Hettinger added the comment:

> The change can break existing code that uses boolean testing 
> instead of checking for None.

For this reason, I think Guido would oppose this proposal.  In the past he has 
objected to iterators having a True boolean value to indicate that there were 
more values available for iteration.  I think similar reasoning applies here.

--
nosy: +rhettinger

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I'm not sure that it is worth to implement the __bool__() method. This doesn't 
add much in comparison with checking the returncode attribute.

The change can break existing code that uses boolean testing instead of 
checking for None.

--

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Sayan Chowdhury]

Changes by Sayan Chowdhury :


--
pull_requests: +273

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


--
versions: +Python 3.7 -Python 3.6

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Sayan Chowdhury]

Sayan Chowdhury added the comment:

I am taking over to do the rest part required for this ticket.

--
nosy: +sayanchowdhury

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Richard Neumann]

Richard Neumann added the comment:

Thank you for the hint.
I never before contributed code to the python foundation and thus am not 
familiar with the process.
I will look into it when I find the time.

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

This is not enough. New feature should be documented (in new method docstring, 
in subprocess documentation and in What's New document) and tested.

And please sign a Contributor Licensing Agreement.

http://www.python.org/psf/contrib/contrib-form/
http://www.python.org/psf/contrib/

--
nosy: +serhiy.storchaka

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Richard Neumann]

Richard Neumann added the comment:

Please excuse my ambiguous phrasing.
What I meant was I created the patch _from_ the Python 3.5.1 module _for_ 
Python 3.6.

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[STINNER Victor]

STINNER Victor added the comment:

It's a new feature, it should only go to Python 3.6.

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Richard Neumann]

Richard Neumann added the comment:

I took the liberty to create a patch for Python v3.5.1.

--
keywords: +patch
nosy: +Richard Neumann
Added file: http://bugs.python.org/file42828/subprocess.patch

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Berker Peksag]

Berker Peksag added the comment:

The idea sounds good to me.

--
nosy: +berker.peksag
stage:  -> needs patch
versions: +Python 3.6 -Python 3.5

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[STINNER Victor]

STINNER Victor added the comment:

Can you please give examples of use cases? (code)

--
nosy: +haypo

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Richard Neumann]

Richard Neumann added the comment:

A useless use case is attached.
Basically it boils down to having the ability to evaluate the CompletedProcess 
directly by if/else rather than comparing its returncode attribute to zero each 
time or handling the exception raised by check_returncode().
I use this quite frequently in programs which run system commands.
Before the new subprocess.run() method and subprocess.CompletedProcess were 
introduced with python 3.5 I already wrote my own library for that, wich now 
nearly became obsoleted by the new subprocess library of python 3.5 with the 
expection that it does not have this feature.
See the class ProcessResult here: 
https://github.com/HOMEINFO/homeinfo-lib/blob/master/homeinfo/lib/system.py

--
Added file: http://bugs.python.org/file40836/usecase.py

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[issue25452] Add __bool__() method to subprocess.CompletedProcess

[Richard Neumann]

New submission from Richard Neumann:

The class subprocess.CompletedProcess is currently lacking a __bool__() method.

It might be a practical feature to have the possibility to evaluate a 
CompletedProcess instance in an if/else block without the necessity to handle 
the exception raised by CompletedProcess.check_returncode().

Hence, I suggest adding the method

def __bool__(self):
return self.returncode == 0

to the class.

--
components: Library (Lib)
messages: 253282
nosy: conqp
priority: normal
severity: normal
status: open
title: Add __bool__() method to subprocess.CompletedProcess
type: enhancement
versions: Python 3.5

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