inspect: Fix getsource() to load updated source of reloaded module

Issue #1218234. Initial patch by Berker Peksag.

Lib/inspect.py

@@ -653,11 +653,17 @@ def findsource(object):
     in the file and the line number indexes a line in that list.  An OSError
     is raised if the source code cannot be retrieved."""
 
-    file = getfile(object)
-    sourcefile = getsourcefile(object)
-    if not sourcefile and file[:1] + file[-1:] != '<>':
-        raise OSError('source code not available')
-    file = sourcefile if sourcefile else file
+    file = getsourcefile(object)
+    if file:
+        # Invalidate cache if needed.
+        linecache.checkcache(file)
+    else:
+        file = getfile(object)
+        # Allow filenames in form of "<something>" to pass through.
+        # `doctest` monkeypatches `linecache` module to enable
+        # inspection, so let `linecache.getlines` to be called.
+        if not (file.startswith('<') and file.endswith('>')):
+            raise OSError('source code not available')
 
     module = getmodule(object, file)
     if module:

Lib/test/test_inspect.py

@@ -14,6 +14,7 @@ import re
 import shutil
 import sys
 import types
+import textwrap
 import unicodedata
 import unittest
 import unittest.mock
@@ -29,6 +30,8 @@ from test.script_helper import assert_python_ok, assert_python_failure
 from test import inspect_fodder as mod
 from test import inspect_fodder2 as mod2
 
+from test.test_import import _ready_to_import
+
 
 # Functions tested in this suite:
 # ismodule, isclass, ismethod, isfunction, istraceback, isframe, iscode,
@@ -3262,6 +3265,34 @@ class TestMain(unittest.TestCase):
         self.assertEqual(err, b'')
 
 
+class TestReload(unittest.TestCase):
+
+    src_before = textwrap.dedent("""\
+def foo():
+    print("Bla")
+    """)
+
+    src_after = textwrap.dedent("""\
+def foo():
+    print("Oh no!")
+    """)
+
+    def assertInspectEqual(self, path, source):
+        inspected_src = inspect.getsource(source)
+        with open(path) as src:
+            self.assertEqual(
+                src.read().splitlines(True),
+                inspected_src.splitlines(True)
+            )
+
+    def test_getsource_reload(self):
+        # see issue 1218234
+        with _ready_to_import('reload_bug', self.src_before) as (name, path):
+            module = importlib.import_module(name)
+            self.assertInspectEqual(path, module)
+            with open(path, 'w') as src:
+                src.write(self.src_after)
+            self.assertInspectEqual(path, module)
 
 
 def test_main():
@@ -3272,7 +3303,7 @@ def test_main():
         TestGetcallargsUnboundMethods, TestGetattrStatic, TestGetGeneratorState,
         TestNoEOL, TestSignatureObject, TestSignatureBind, TestParameterObject,
         TestBoundArguments, TestSignaturePrivateHelpers, TestGetClosureVars,
-        TestUnwrap, TestMain
+        TestUnwrap, TestMain, TestReload
     )
 
 if __name__ == "__main__":

Misc/NEWS

@@ -194,6 +194,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #1218234: Fix inspect.getsource() to load updated source of
+  reloaded module. Initial patch by Berker Peksag.
+
 - Issue #21740: Support wrapped callables in pydoc. Patch by Claudiu Popa.
 
 - Issue #23009: Make sure selectors.EpollSelecrtor.select() works when no