Source code for _pytest.capture

per-test stdout/stderr capturing mechanism.

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import collections
import contextlib
import io
import os
import sys
from io import UnsupportedOperation
from tempfile import TemporaryFile

import six

import pytest
from _pytest.compat import _PY3
from _pytest.compat import CaptureIO

patchsysdict = {0: "stdin", 1: "stdout", 2: "stderr"}

def pytest_addoption(parser):
    group = parser.getgroup("general")
        default="fd" if hasattr(os, "dup") else "sys",
        choices=["fd", "sys", "no"],
        help="per-test capturing method: one of fd|sys|no.",
        help="shortcut for --capture=no.",

def pytest_load_initial_conftests(early_config, parser, args):
    ns = early_config.known_args_namespace
    if ns.capture == "fd":
    pluginmanager = early_config.pluginmanager
    capman = CaptureManager(ns.capture)
    pluginmanager.register(capman, "capturemanager")

    # make sure that capturemanager is properly reset at final shutdown

    # make sure logging does not raise exceptions at the end
    def silence_logging_at_shutdown():
        if "logging" in sys.modules:
            sys.modules["logging"].raiseExceptions = False


    # finally trigger conftest loading but while capturing (issue93)
    outcome = yield
    if outcome.excinfo is not None:
        out, err = capman.read_global_capture()

class CaptureManager(object):
    Capture plugin, manages that the appropriate capture method is enabled/disabled during collection and each
    test phase (setup, call, teardown). After each of those points, the captured output is obtained and
    attached to the collection/runtest report.

    There are two levels of capture:
    * global: which is enabled by default and can be suppressed by the ``-s`` option. This is always enabled/disabled
      during collection and each test phase.
    * fixture: when a test function or one of its fixture depend on the ``capsys`` or ``capfd`` fixtures. In this
      case special handling is needed to ensure the fixtures take precedence over the global capture.

    def __init__(self, method):
        self._method = method
        self._global_capturing = None
        self._current_item = None

    def __repr__(self):
        return "<CaptureManager _method=%r _global_capturing=%r _current_item=%r>" % (

    def _getcapture(self, method):
        if method == "fd":
            return MultiCapture(out=True, err=True, Capture=FDCapture)
        elif method == "sys":
            return MultiCapture(out=True, err=True, Capture=SysCapture)
        elif method == "no":
            return MultiCapture(out=False, err=False, in_=False)
        raise ValueError("unknown capturing method: %r" % method)  # pragma: no cover

    def is_capturing(self):
        if self.is_globally_capturing():
            return "global"
        capture_fixture = getattr(self._current_item, "_capture_fixture", None)
        if capture_fixture is not None:
            return (
                "fixture %s" % self._current_item._capture_fixture.request.fixturename
        return False

    # Global capturing control

    def is_globally_capturing(self):
        return self._method != "no"

    def start_global_capturing(self):
        assert self._global_capturing is None
        self._global_capturing = self._getcapture(self._method)

    def stop_global_capturing(self):
        if self._global_capturing is not None:
            self._global_capturing = None

    def resume_global_capture(self):
        # During teardown of the python process, and on rare occasions, capture
        # attributes can be `None` while trying to resume global capture.
        if self._global_capturing is not None:

    def suspend_global_capture(self, in_=False):
        cap = getattr(self, "_global_capturing", None)
        if cap is not None:

    def suspend(self, in_=False):
        # Need to undo local capsys-et-al if it exists before disabling global capture.

    def resume(self):

    def read_global_capture(self):
        return self._global_capturing.readouterr()

    # Fixture Control (it's just forwarding, think about removing this later)

    def activate_fixture(self, item):
        """If the current item is using ``capsys`` or ``capfd``, activate them so they take precedence over
        the global capture.
        fixture = getattr(item, "_capture_fixture", None)
        if fixture is not None:

    def deactivate_fixture(self, item):
        """Deactivates the ``capsys`` or ``capfd`` fixture of this item, if any."""
        fixture = getattr(item, "_capture_fixture", None)
        if fixture is not None:

    def suspend_fixture(self, item):
        fixture = getattr(item, "_capture_fixture", None)
        if fixture is not None:

    def resume_fixture(self, item):
        fixture = getattr(item, "_capture_fixture", None)
        if fixture is not None:

    # Helper context managers

    def global_and_fixture_disabled(self):
        """Context manager to temporarily disable global and current fixture capturing."""

    def item_capture(self, when, item):

        out, err = self.read_global_capture()
        item.add_report_section(when, "stdout", out)
        item.add_report_section(when, "stderr", err)

    # Hooks

    def pytest_make_collect_report(self, collector):
        if isinstance(collector, pytest.File):
            outcome = yield
            out, err = self.read_global_capture()
            rep = outcome.get_result()
            if out:
                rep.sections.append(("Captured stdout", out))
            if err:
                rep.sections.append(("Captured stderr", err))

    def pytest_runtest_protocol(self, item):
        self._current_item = item
        self._current_item = None

    def pytest_runtest_setup(self, item):
        with self.item_capture("setup", item):

    def pytest_runtest_call(self, item):
        with self.item_capture("call", item):

    def pytest_runtest_teardown(self, item):
        with self.item_capture("teardown", item):

    def pytest_keyboard_interrupt(self, excinfo):

    def pytest_internalerror(self, excinfo):

capture_fixtures = {"capfd", "capfdbinary", "capsys", "capsysbinary"}

def _ensure_only_one_capture_fixture(request, name):
    fixtures = set(request.fixturenames) & capture_fixtures - {name}
    if fixtures:
        fixtures = sorted(fixtures)
        fixtures = fixtures[0] if len(fixtures) == 1 else fixtures
        raise request.raiseerror(
            "cannot use {} and {} at the same time".format(fixtures, name)

[docs]@pytest.fixture def capsys(request): """Enable text capturing of writes to ``sys.stdout`` and ``sys.stderr``. The captured output is made available via ``capsys.readouterr()`` method calls, which return a ``(out, err)`` namedtuple. ``out`` and ``err`` will be ``text`` objects. """ _ensure_only_one_capture_fixture(request, "capsys") with _install_capture_fixture_on_item(request, SysCapture) as fixture: yield fixture
[docs]@pytest.fixture def capsysbinary(request): """Enable bytes capturing of writes to ``sys.stdout`` and ``sys.stderr``. The captured output is made available via ``capsysbinary.readouterr()`` method calls, which return a ``(out, err)`` namedtuple. ``out`` and ``err`` will be ``bytes`` objects. """ _ensure_only_one_capture_fixture(request, "capsysbinary") # Currently, the implementation uses the python3 specific `.buffer` # property of CaptureIO. if sys.version_info < (3,): raise request.raiseerror("capsysbinary is only supported on Python 3") with _install_capture_fixture_on_item(request, SysCaptureBinary) as fixture: yield fixture
[docs]@pytest.fixture def capfd(request): """Enable text capturing of writes to file descriptors ``1`` and ``2``. The captured output is made available via ``capfd.readouterr()`` method calls, which return a ``(out, err)`` namedtuple. ``out`` and ``err`` will be ``text`` objects. """ _ensure_only_one_capture_fixture(request, "capfd") if not hasattr(os, "dup"): pytest.skip( "capfd fixture needs os.dup function which is not available in this system" ) with _install_capture_fixture_on_item(request, FDCapture) as fixture: yield fixture
[docs]@pytest.fixture def capfdbinary(request): """Enable bytes capturing of writes to file descriptors ``1`` and ``2``. The captured output is made available via ``capfd.readouterr()`` method calls, which return a ``(out, err)`` namedtuple. ``out`` and ``err`` will be ``byte`` objects. """ _ensure_only_one_capture_fixture(request, "capfdbinary") if not hasattr(os, "dup"): pytest.skip( "capfdbinary fixture needs os.dup function which is not available in this system" ) with _install_capture_fixture_on_item(request, FDCaptureBinary) as fixture: yield fixture
@contextlib.contextmanager def _install_capture_fixture_on_item(request, capture_class): """ Context manager which creates a ``CaptureFixture`` instance and "installs" it on the item/node of the given request. Used by ``capsys`` and ``capfd``. The CaptureFixture is added as attribute of the item because it needs to accessed by ``CaptureManager`` during its ``pytest_runtest_*`` hooks. """ request.node._capture_fixture = fixture = CaptureFixture(capture_class, request) capmanager = request.config.pluginmanager.getplugin("capturemanager") # Need to active this fixture right away in case it is being used by another fixture (setup phase). # If this fixture is being used only by a test function (call phase), then we wouldn't need this # activation, but it doesn't hurt. capmanager.activate_fixture(request.node) yield fixture fixture.close() del request.node._capture_fixture
[docs]class CaptureFixture(object): """ Object returned by :py:func:`capsys`, :py:func:`capsysbinary`, :py:func:`capfd` and :py:func:`capfdbinary` fixtures. """ def __init__(self, captureclass, request): self.captureclass = captureclass self.request = request self._capture = None self._captured_out = self.captureclass.EMPTY_BUFFER self._captured_err = self.captureclass.EMPTY_BUFFER def _start(self): # Start if not started yet if getattr(self, "_capture", None) is None: self._capture = MultiCapture( out=True, err=True, in_=False, Capture=self.captureclass ) self._capture.start_capturing() def close(self): if self._capture is not None: out, err = self._capture.pop_outerr_to_orig() self._captured_out += out self._captured_err += err self._capture.stop_capturing() self._capture = None
[docs] def readouterr(self): """Read and return the captured output so far, resetting the internal buffer. :return: captured content as a namedtuple with ``out`` and ``err`` string attributes """ captured_out, captured_err = self._captured_out, self._captured_err if self._capture is not None: out, err = self._capture.readouterr() captured_out += out captured_err += err self._captured_out = self.captureclass.EMPTY_BUFFER self._captured_err = self.captureclass.EMPTY_BUFFER return CaptureResult(captured_out, captured_err)
def _suspend(self): """Suspends this fixture's own capturing temporarily.""" self._capture.suspend_capturing() def _resume(self): """Resumes this fixture's own capturing temporarily.""" self._capture.resume_capturing()
[docs] @contextlib.contextmanager def disabled(self): """Temporarily disables capture while inside the 'with' block.""" capmanager = self.request.config.pluginmanager.getplugin("capturemanager") with capmanager.global_and_fixture_disabled(): yield
def safe_text_dupfile(f, mode, default_encoding="UTF8"): """ return an open text file object that's a duplicate of f on the FD-level if possible. """ encoding = getattr(f, "encoding", None) try: fd = f.fileno() except Exception: if "b" not in getattr(f, "mode", "") and hasattr(f, "encoding"): # we seem to have a text stream, let's just use it return f else: newfd = os.dup(fd) if "b" not in mode: mode += "b" f = os.fdopen(newfd, mode, 0) # no buffering return EncodedFile(f, encoding or default_encoding) class EncodedFile(object): errors = "strict" # possibly needed by py3 code (issue555) def __init__(self, buffer, encoding): self.buffer = buffer self.encoding = encoding def write(self, obj): if isinstance(obj, six.text_type): obj = obj.encode(self.encoding, "replace") elif _PY3: raise TypeError( "write() argument must be str, not {}".format(type(obj).__name__) ) self.buffer.write(obj) def writelines(self, linelist): data = "".join(linelist) self.write(data) @property def name(self): """Ensure that is a string.""" return repr(self.buffer) def __getattr__(self, name): return getattr(object.__getattribute__(self, "buffer"), name) CaptureResult = collections.namedtuple("CaptureResult", ["out", "err"]) class MultiCapture(object): out = err = in_ = None def __init__(self, out=True, err=True, in_=True, Capture=None): if in_: self.in_ = Capture(0) if out: self.out = Capture(1) if err: self.err = Capture(2) def __repr__(self): return "<MultiCapture out=%r err=%r in_=%r>" % (self.out, self.err, self.in_) def start_capturing(self): if self.in_: self.in_.start() if self.out: self.out.start() if self.err: self.err.start() def pop_outerr_to_orig(self): """ pop current snapshot out/err capture and flush to orig streams. """ out, err = self.readouterr() if out: self.out.writeorg(out) if err: self.err.writeorg(err) return out, err def suspend_capturing(self, in_=False): if self.out: self.out.suspend() if self.err: self.err.suspend() if in_ and self.in_: self.in_.suspend() self._in_suspended = True def resume_capturing(self): if self.out: self.out.resume() if self.err: self.err.resume() if hasattr(self, "_in_suspended"): self.in_.resume() del self._in_suspended def stop_capturing(self): """ stop capturing and reset capturing streams """ if hasattr(self, "_reset"): raise ValueError("was already stopped") self._reset = True if self.out: self.out.done() if self.err: self.err.done() if self.in_: self.in_.done() def readouterr(self): """ return snapshot unicode value of stdout/stderr capturings. """ return CaptureResult( self.out.snap() if self.out is not None else "", self.err.snap() if self.err is not None else "", ) class NoCapture(object): EMPTY_BUFFER = None __init__ = start = done = suspend = resume = lambda *args: None class FDCaptureBinary(object): """Capture IO to/from a given os-level filedescriptor. snap() produces `bytes` """ EMPTY_BUFFER = b"" def __init__(self, targetfd, tmpfile=None): self.targetfd = targetfd try: self.targetfd_save = os.dup(self.targetfd) except OSError: self.start = lambda: None self.done = lambda: None else: if targetfd == 0: assert not tmpfile, "cannot set tmpfile with stdin" tmpfile = open(os.devnull, "r") self.syscapture = SysCapture(targetfd) else: if tmpfile is None: f = TemporaryFile() with f: tmpfile = safe_text_dupfile(f, mode="wb+") if targetfd in patchsysdict: self.syscapture = SysCapture(targetfd, tmpfile) else: self.syscapture = NoCapture() self.tmpfile = tmpfile self.tmpfile_fd = tmpfile.fileno() def __repr__(self): return "<FDCapture %s oldfd=%s>" % ( self.targetfd, getattr(self, "targetfd_save", None), ) def start(self): """ Start capturing on targetfd using memorized tmpfile. """ try: os.fstat(self.targetfd_save) except (AttributeError, OSError): raise ValueError("saved filedescriptor not valid anymore") os.dup2(self.tmpfile_fd, self.targetfd) self.syscapture.start() def snap(self): res = self.tmpfile.truncate() return res def done(self): """ stop capturing, restore streams, return original capture file, seeked to position zero. """ targetfd_save = self.__dict__.pop("targetfd_save") os.dup2(targetfd_save, self.targetfd) os.close(targetfd_save) self.syscapture.done() _attempt_to_close_capture_file(self.tmpfile) def suspend(self): self.syscapture.suspend() os.dup2(self.targetfd_save, self.targetfd) def resume(self): self.syscapture.resume() os.dup2(self.tmpfile_fd, self.targetfd) def writeorg(self, data): """ write to original file descriptor. """ if isinstance(data, six.text_type): data = data.encode("utf8") # XXX use encoding of original stream os.write(self.targetfd_save, data) class FDCapture(FDCaptureBinary): """Capture IO to/from a given os-level filedescriptor. snap() produces text """ EMPTY_BUFFER = str() def snap(self): res = super(FDCapture, self).snap() enc = getattr(self.tmpfile, "encoding", None) if enc and isinstance(res, bytes): res = six.text_type(res, enc, "replace") return res class SysCapture(object): EMPTY_BUFFER = str() def __init__(self, fd, tmpfile=None): name = patchsysdict[fd] self._old = getattr(sys, name) = name if tmpfile is None: if name == "stdin": tmpfile = DontReadFromInput() else: tmpfile = CaptureIO() self.tmpfile = tmpfile def start(self): setattr(sys,, self.tmpfile) def snap(self): res = self.tmpfile.getvalue() self.tmpfile.truncate() return res def done(self): setattr(sys,, self._old) del self._old _attempt_to_close_capture_file(self.tmpfile) def suspend(self): setattr(sys,, self._old) def resume(self): setattr(sys,, self.tmpfile) def writeorg(self, data): self._old.write(data) self._old.flush() class SysCaptureBinary(SysCapture): EMPTY_BUFFER = b"" def snap(self): res = self.tmpfile.buffer.getvalue() self.tmpfile.truncate() return res class DontReadFromInput(six.Iterator): """Temporary stub class. Ideally when stdin is accessed, the capturing should be turned off, with possibly all data captured so far sent to the screen. This should be configurable, though, because in automated test runs it is better to crash than hang indefinitely. """ encoding = None def read(self, *args): raise IOError("reading from stdin while output is captured") readline = read readlines = read __next__ = read def __iter__(self): return self def fileno(self): raise UnsupportedOperation("redirected stdin is pseudofile, has no fileno()") def isatty(self): return False def close(self): pass @property def buffer(self): if sys.version_info >= (3, 0): return self else: raise AttributeError("redirected stdin has no attribute buffer") def _colorama_workaround(): """ Ensure colorama is imported so that it attaches to the correct stdio handles on Windows. colorama uses the terminal on import time. So if something does the first import of colorama while I/O capture is active, colorama will fail in various ways. """ if sys.platform.startswith("win32"): try: import colorama # noqa: F401 except ImportError: pass def _readline_workaround(): """ Ensure readline is imported so that it attaches to the correct stdio handles on Windows. Pdb uses readline support where available--when not running from the Python prompt, the readline module is not imported until running the pdb REPL. If running pytest with the --pdb option this means the readline module is not imported until after I/O capture has been started. This is a problem for pyreadline, which is often used to implement readline support on Windows, as it does not attach to the correct handles for stdout and/or stdin if they have been redirected by the FDCapture mechanism. This workaround ensures that readline is imported before I/O capture is setup so that it can attach to the actual stdin/out for the console. See """ if sys.platform.startswith("win32"): try: import readline # noqa: F401 except ImportError: pass def _py36_windowsconsoleio_workaround(stream): """ Python 3.6 implemented unicode console handling for Windows. This works by reading/writing to the raw console handle using ``{Read,Write}ConsoleW``. The problem is that we are going to ``dup2`` over the stdio file descriptors when doing ``FDCapture`` and this will ``CloseHandle`` the handles used by Python to write to the console. Though there is still some weirdness and the console handle seems to only be closed randomly and not on the first call to ``CloseHandle``, or maybe it gets reopened with the same handle value when we suspend capturing. The workaround in this case will reopen stdio with a different fd which also means a different handle by replicating the logic in "Py_lifecycle.c:initstdio/create_stdio". :param stream: in practice ``sys.stdout`` or ``sys.stderr``, but given here as parameter for unittesting purposes. See """ if not sys.platform.startswith("win32") or sys.version_info[:2] < (3, 6): return # bail out if ``stream`` doesn't seem like a proper ``io`` stream (#2666) if not hasattr(stream, "buffer"): return buffered = hasattr(stream.buffer, "raw") raw_stdout = stream.buffer.raw if buffered else stream.buffer if not isinstance(raw_stdout, io._WindowsConsoleIO): return def _reopen_stdio(f, mode): if not buffered and mode[0] == "w": buffering = 0 else: buffering = -1 return io.TextIOWrapper( open(os.dup(f.fileno()), mode, buffering), f.encoding, f.errors, f.newlines, f.line_buffering, ) sys.stdin = _reopen_stdio(sys.stdin, "rb") sys.stdout = _reopen_stdio(sys.stdout, "wb") sys.stderr = _reopen_stdio(sys.stderr, "wb") def _attempt_to_close_capture_file(f): """Suppress IOError when closing the temporary file used for capturing streams in py27 (#2370)""" if six.PY2: try: f.close() except IOError: pass else: f.close()