capsys breaks sys.stdin.encoding

[kpinc]

Hi,

Using capsys breaks the use of sys.stdin.encoding. (And probably does the same for sys.stdout.encoding and other file like object encoding attributes.)

Using sys.stdout.encoding is important when writing portable code that sometimes outputs stdout to the MS Windows console, which may use cp1252 encoding. If you don't explicitly do something to encode your unicode strings and handle encoding failures then printing sometimes crashes your program with a UnicodeEncodeError exception. But testing sys.stdout.encoding with capsys is awkward.

See the example.

$ venv/bin/pip list
DEPRECATION: The default format will switch to columns in the future. You can use --format=(legacy|columns) (or define a format=(legacy|columns) in your pip.conf under the [list] section) to disable this warning.
appdirs (1.4.3)
packaging (16.8)
pip (9.0.1)
py (1.4.33)
pyparsing (2.2.0)
pytest (3.0.7)
setuptools (35.0.1)
six (1.10.0)

Debian stable 8.7 (Jessie)
Python 2.7.9 (from Debian repo)
(You get the same output from Debian's Python 3.4.2.)

#src/test_capsys.py 
from __future__ import print_function

import sys


def func(text):
    print(text.encode(sys.stdout.encoding, 'replace'))


def test_func(capsys):
    func('sample text')
    (out, err) = capsys.readouterr()
    assert out
    assert err == ''

$ venv/bin/pytest 
============================= test session starts ==============================
platform linux2 -- Python 2.7.9, pytest-3.0.7, py-1.4.33, pluggy-0.4.0
rootdir: *REDACTED*, inifile:
collected 1 items 

src/test_capsys.py F

=================================== FAILURES ===================================
__________________________________ test_func ___________________________________

capsys = <_pytest.capture.CaptureFixture instance at 0x7f90ba65a8c0>

    def test_func(capsys):
>       func('sample text')

src/test_capsys.py:11: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

text = 'sample text'

    def func(text):
>       print(text.encode(sys.stdout.encoding, 'replace'))
E       TypeError: encode() argument 1 must be string, not None

src/test_capsys.py:7: TypeError
=========================== 1 failed in 0.40 seconds ===========================

EDIT: fixed formatting

[nicoddemus]

Thanks for the report!

It seems it should be just a matter of copying the encoding attribute from the original stream.

[kpinc]

On Thu, 20 Apr 2017 04:19:54 -0700 Bruno Oliveira ***@***.***> wrote: It seems it should be just a matter of copying the `encoding` attribute from the original stream.

Makes sense to me. :) Karl <kop@meme.com> Free Software: "You don't pay back, you pay forward." -- Robert A. Heinlein

[kpinc]

On Thu, 20 Apr 2017 04:19:54 -0700 Bruno Oliveira ***@***.***> wrote: It seems it should be just a matter of copying the `encoding` attribute from the original stream.

You probably also want to copy the "read-only-ness", if any, of the original stream's `encoding` attribute. Karl <kop@meme.com> Free Software: "You don't pay back, you pay forward." -- Robert A. Heinlein

[maiksensi]

I could only reproduce this for py27 running it via: tox -e py27,py34,py36,py35 -- testcases/test_capsys.py.

ERROR:   py27: commands failed
  py34: commands succeeded
  py36: commands succeeded
  py35: commands succeeded

The py27 outout is:

testcases/test_capsys.py F
==================================================================================================== short test summary info =====================================================================================================
FAIL testcases/test_capsys.py::test_func

============================================================================================================ FAILURES ============================================================================================================
___________________________________________________________________________________________________________ test_func ____________________________________________________________________________________________________________

capsys = <_pytest.capture.CaptureFixture instance at 0x7f4fc750d680>

    def test_func(capsys):
>       func('sample text')

testcases/test_capsys.py:12: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

text = 'sample text'

    def func(text):
>       print(text.encode(sys.stdout.encoding, 'replace'))
E       TypeError: encode() argument 1 must be string, not None

testcases/test_capsys.py:8: TypeError
==================================================================================================== 1 failed in 0.05 seconds ====================================================================================================
ERROR: InvocationError: '/home/maiksen/repos/pytest/.tox/py27/bin/pytest --lsof -rfsxX testcases/test_capsys.py'

I am on the latest py3.4 available and on ubuntu 16.04.

This doesnt probably change the suggestions on what to change to fix the issue.