Capture and log messages emitted by C modules when importing them

ChangeLog

@@ -15,6 +15,11 @@ Release date: TBA
 
   Closes #1512
 
+* Capture and log messages emitted by C extensions when importing them.
+  This prevents contaminating programmatic output, e.g. pylint's JSON reporter.
+
+  Closes PyCQA/pylint#3518
+
 * Remove dependency on ``pkg_resources`` from ``setuptools``.
 
   Closes #1103

astroid/modutils.py

@@ -19,17 +19,23 @@
 import importlib
 import importlib.machinery
 import importlib.util
+import io
 import itertools
+import logging
 import os
 import sys
 import sysconfig
 import types
+from contextlib import redirect_stderr, redirect_stdout
 from functools import lru_cache
 from pathlib import Path
 
 from astroid.const import IS_JYTHON, IS_PYPY
 from astroid.interpreter._import import spec, util
 
+logger = logging.getLogger(__name__)
+
+
 if sys.platform.startswith("win"):
     PY_SOURCE_EXTS = ("py", "pyw")
     PY_COMPILED_EXTS = ("dll", "pyd")
@@ -171,7 +177,25 @@ def load_module_from_name(dotted_name: str) -> types.ModuleType:
     except KeyError:
         pass
 
-    return importlib.import_module(dotted_name)
+    # Capture and log anything emitted during import to avoid
+    # contaminating JSON reports in pylint
+    with redirect_stderr(io.StringIO()) as stderr, redirect_stdout(
+        io.StringIO()
+    ) as stdout:
+        module = importlib.import_module(dotted_name)
+
+    stderr_value = stderr.getvalue()
+    if stderr_value:
+        logger.error(
+            "Captured stderr while importing %s:\n%s", dotted_name, stderr_value
+        )
+    stdout_value = stdout.getvalue()
+    if stdout_value:
+        logger.info(
+            "Captured stdout while importing %s:\n%s", dotted_name, stdout_value
+        )
+
+    return module
 
 
 def load_module_from_modpath(parts):

tests/unittest_modutils.py

@@ -6,6 +6,7 @@
 unit tests for module modutils (module manipulation utilities)
 """
 import email
+import logging
 import os
 import shutil
 import sys
@@ -16,6 +17,8 @@
 from xml import etree
 from xml.etree import ElementTree
 
+from pytest import CaptureFixture, LogCaptureFixture
+
 import astroid
 from astroid import modutils
 from astroid.interpreter._import import spec
@@ -57,7 +60,7 @@ def test_find_egg_module(self) -> None:
 
 
 class LoadModuleFromNameTest(unittest.TestCase):
-    """load a python module from it's name"""
+    """load a python module from its name"""
 
     def test_known_values_load_module_from_name_1(self) -> None:
         self.assertEqual(modutils.load_module_from_name("sys"), sys)
@@ -71,6 +74,38 @@ def test_raise_load_module_from_name_1(self) -> None:
         )
 
 
+def test_import_dotted_library(
+    capsys: CaptureFixture,
+    caplog: LogCaptureFixture,
+) -> None:
+    caplog.set_level(logging.INFO)
+    original_module = sys.modules.pop("xml.etree.ElementTree")
+    expected_out = "INFO (TEST): Welcome to cElementTree!"
+    expected_err = "WARNING (TEST): Monkey-patched version of cElementTree"
+
+    def function_with_stdout_and_stderr(expected_out, expected_err):
+        def mocked_function(*args, **kwargs):
+            print(f"{expected_out} args={args} kwargs={kwargs}")
+            print(expected_err, file=sys.stderr)
+
+        return mocked_function
+
+    try:
+        with unittest.mock.patch(
+            "importlib.import_module",
+            side_effect=function_with_stdout_and_stderr(expected_out, expected_err),
+        ):
+            modutils.load_module_from_name("xml.etree.ElementTree")
+
+        out, err = capsys.readouterr()
+        assert expected_out in caplog.text
+        assert expected_err in caplog.text
+        assert not out
+        assert not err
+    finally:
+        sys.modules["xml.etree.ElementTree"] = original_module
+
+
 class GetModulePartTest(unittest.TestCase):
     """given a dotted name return the module part of the name"""