How to print to console in pytest

Question

I m trying to use TDD  test-driven development  with pytest  pytest will not print to the console when I use print   I am using pytest my tests py to run it   The documentation seems to say that it should work by default  http   pytest org latest capture html  But   import myapplication as tum  class TestBlogger        classmethod     def setup class self           self user    alice          self b   tum Blogger self user          print  This should be printed  but it won t be        def test inherit self           assert issubclass tum Blogger  tum Site          links   self b get links posts          print len links      This won t print either    Nothing gets printed to my standard output console  just the normal progress and how many many tests passed failed    And the script that I m testing contains print   class Blogger Site       get links self  posts           print len posts      It won t get printed in the test    In unittest module  everything gets printed by default  which is exactly what I need  However  I wish to use pytest for other reasons   Does anyone know how to make the print statements get shown

User · Answer

I needed to print important warning about skipped tests exactly when PyTest muted literally everything.

I didn't want to fail a test to send a signal, so I did a hack as follow:

def test_2_YellAboutBrokenAndMutedTests():
    import atexit
    def report():
        print C_patch.tidy_text("""
In silent mode PyTest breaks low level stream structure I work with, so
I cannot test if my functionality work fine. I skipped corresponding tests.
Run `py.test -s` to make sure everything is tested.""")
    if sys.stdout != sys.__stdout__:
        atexit.register(report)

The atexit module allows me to print stuff after PyTest released the output streams. The output looks as follow:

============================= test session starts ==============================
platform linux2 -- Python 2.7.3, pytest-2.9.2, py-1.4.31, pluggy-0.3.1
rootdir: /media/Storage/henaro/smyth/Alchemist2-git/sources/C_patch, inifile: 
collected 15 items 

test_C_patch.py .....ssss....s.

===================== 10 passed, 5 skipped in 0.15 seconds =====================
In silent mode PyTest breaks low level stream structure I work with, so
I cannot test if my functionality work fine. I skipped corresponding tests.
Run `py.test -s` to make sure everything is tested.
~/.../sources/C_patch$

Message is printed even when PyTest is in silent mode, and is not printed if you run stuff with py.test -s, so everything is tested nicely already.

User · Answer

By default  py test captures the result of standard out so that it can control how it prints it out  If it didn t do this  it would spew out a lot of text without the context of what test printed that text   However  if a test fails  it will include a section in the resulting report that shows what was printed to standard out in that particular test   For example   def test good        for i in range 1000           print i   def test bad        print  this should fail        assert False   Results in the following output    gt  gt  gt  py test tmp py                               test session starts                                platform darwin -- Python 2 7 6 -- py-1 4 20 -- pytest-2 5 2 plugins  cache  cov  pep8  xdist collected 2 items  tmp py  F                                      FAILURES                                                                         test bad                                          def test bad            print  this should fail     gt        assert False E       assert False  tmp py 7  AssertionError ------------------------------- Captured stdout -------------------------------- this should fail                         1 failed  1 passed in 0 04 seconds                          Note the Captured stdout section   If you would like to see print statements as they are executed  you can pass the -s flag to py test  However  note that this can sometimes be difficult to parse    gt  gt  gt  py test tmp py -s                               test session starts                                platform darwin -- Python 2 7 6 -- py-1 4 20 -- pytest-2 5 2 plugins  cache  cov  pep8  xdist collected 2 items  tmp py 0 1 2 3     and so on     997 998 999  this should fail  F                                      FAILURES                                                                         test bad                                          def test bad            print  this should fail     gt        assert False E       assert False  tmp py 7  AssertionError                        1 failed  1 passed in 0 02 seconds

User · Answer

Using -s option will print output of all functions  which may be too much    If you need particular output  the doc page you mentioned offers few suggestions    Insert assert False   dumb assert to make PyTest print my stuff  at the end of your function  and you will see your output due to failed test  You have special object passed to you by PyTest  and you can write the output into a file to inspect it later  like  def test good1 capsys       for i in range 5           print i     out  err   capsys readouterr       open  err txt    w   write err      open  out txt    w   write out    You can open the out and err files in a separate tab and let editor automatically refresh it for you  or do a simple py test  cat out txt shell command to run your test    That is rather hackish way to do stuff  but may be it is the stuff you need  after all  TDD means you mess with stuff and leave it clean and silent when it s ready  -

User · Answer

I originally came in here to find how to make PyTest print in VSCode s console while running debugging the unit test from there  This can be done with the following launch json configuration  Given  venv the virtual environment folder        version    0 2 0        configurations                            name    PyTest                type    python                request    launch                stopOnEntry   false               pythonPath      config python pythonPath                 module    pytest                args                      -sv                              cwd      workspaceRoot                 env                    envFile      workspaceRoot   venv                debugOptions                      WaitOnAbnormalExit                    WaitOnNormalExit                    RedirectOutput

User · Answer

Short Answer  Use the -s option   pytest -s   Detailed answer  From the docs      During test execution any output sent to stdout and stderr is captured  If a test or a setup method fails its according captured output will usually be shown along with the failure traceback     pytest has the option --capture method in which method is per-test capturing method  and could be one of the following  fd  sys or no  pytest also has the option -s which is a shortcut for --capture no  and this is the option that will allow you to see your print statements in the console   pytest --capture no       show print statements in console pytest -s                 equivalent to previous command   Setting capturing methods or disabling capturing  There are two ways in which pytest can perform capturing    file descriptor  FD  level capturing  default   All writes going to the operating system file descriptors 1 and 2 will be captured  sys level capturing  Only writes to Python files sys stdout and sys stderr will be captured  No capturing of writes to filedescriptors is performed    pytest -s              disable all capturing pytest --capture sys   replace sys stdout stderr with in-mem files pytest --capture fd    also point filedescriptors 1 and 2 to temp file

User · Answer

According to the pytest docs  pytest --capture sys should work  If you want to capture standard out inside a test  refer to the capsys fixture

[python] How to print to console in pytest?

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