Changes to debug() function:

* use str() if exception derives from OSError / EnvironmentError. This
way we will print the file name (if it exists).
* use repr() for any other exception
* add tests for debug() function
* backport contextlib.redirect_stderr

Signed-off-by: Giampaolo Rodola <g.rodola@gmail.com>

3 files changed, 53 insertions, 1 deletions

diff --git a/psutil/_common.py b/psutil/_common.py
index a2b8bab6..6a2f38e1 100644
--- a/psutil/_common.py
+++ b/psutil/_common.py
@@ -837,7 +837,11 @@ if bool(os.getenv('PSUTIL_DEBUG', 0)):
         fname, lineno, func_name, lines, index = inspect.getframeinfo(
             inspect.currentframe().f_back)
         if isinstance(msg, Exception):
-            msg = "ignoring %s" % msg
+            if isinstance(msg, (OSError, IOError, EnvironmentError)):
+                # ...because str(exc) may contain info about the file name
+                msg = "ignoring %s" % msg
+            else:
+                msg = "ignoring %r" % msg
         print("psutil-debug [%s:%s]> %s" % (fname, lineno, msg),  # NOQA
               file=sys.stderr)
 else:
diff --git a/psutil/_compat.py b/psutil/_compat.py
index 90938687..e5275f5f 100644
--- a/psutil/_compat.py
+++ b/psutil/_compat.py
@@ -8,6 +8,7 @@ Python 3 way of doing things).
 """
 
 import collections
+import contextlib
 import errno
 import functools
 import os
@@ -25,6 +26,8 @@ __all__ = [
     "lru_cache",
     # shutil module
     "which", "get_terminal_size",
+    # contextlib module
+    "redirect_stderr",
     # python 3 exceptions
     "FileNotFoundError", "PermissionError", "ProcessLookupError",
     "InterruptedError", "ChildProcessError", "FileExistsError"]
@@ -430,3 +433,17 @@ try:
 except ImportError:
     class SubprocessTimeoutExpired:
         pass
+
+
+# python 3.5
+try:
+    from contextlib import redirect_stderr
+except ImportError:
+    @contextlib.contextmanager
+    def redirect_stderr(new_target):
+        original = getattr(sys, "stderr")
+        try:
+            setattr(sys, "stderr", new_target)
+            yield new_target
+        finally:
+            setattr(sys, "stderr", original)
diff --git a/psutil/tests/test_misc.py b/psutil/tests/test_misc.py
index fc9f5b13..70f6a37e 100755
--- a/psutil/tests/test_misc.py
+++ b/psutil/tests/test_misc.py
@@ -22,11 +22,13 @@ import sys
 from psutil import LINUX
 from psutil import POSIX
 from psutil import WINDOWS
+from psutil._common import debug
 from psutil._common import memoize
 from psutil._common import memoize_when_activated
 from psutil._common import supports_ipv6
 from psutil._common import wrap_numbers
 from psutil._compat import PY3
+from psutil._compat import redirect_stderr
 from psutil.tests import APPVEYOR
 from psutil.tests import CI_TESTING
 from psutil.tests import HAS_BATTERY
@@ -401,6 +403,35 @@ class TestMisc(PsutilTestCase):
                 reload_module(psutil)
             self.assertIn("version conflict", str(cm.exception).lower())
 
+    def test_debug(self):
+        if PY3:
+            from io import StringIO
+        else:
+            from StringIO import StringIO
+
+        with redirect_stderr(StringIO()) as f:
+            debug("hello")
+        msg = f.getvalue()
+        assert msg.startswith("psutil-debug"), msg
+        self.assertIn("hello", msg)
+        self.assertIn(__file__, msg)
+
+        # supposed to use repr(exc)
+        with redirect_stderr(StringIO()) as f:
+            debug(ValueError("this is an error"))
+        msg = f.getvalue()
+        self.assertIn("ignoring ValueError", msg)
+        self.assertIn("'this is an error'", msg)
+
+        # supposed to use str(exc), because of extra info about file name
+        with redirect_stderr(StringIO()) as f:
+            exc = OSError(2, "no such file")
+            exc.filename = "/foo"
+            debug(exc)
+        msg = f.getvalue()
+        self.assertIn("no such file", msg)
+        self.assertIn("/foo", msg)
+
 
 # ===================================================================
 # --- Tests for wrap_numbers() function.