Document why invalidate_caches needed

thomasballinger · thomasballinger · commit 9966986583cf · 2015-12-06T16:18:54.000-05:00
diff --git a/bpython/test/test_curtsies_repl.py b/bpython/test/test_curtsies_repl.py
@@ -297,6 +297,19 @@ def setUp(self):
         self.open = partial(io.open, mode='wt', encoding='utf-8')
         self.dont_write_bytecode = sys.dont_write_bytecode
         sys.dont_write_bytecode = True
+
+        # Because these tests create Python source files at runtime,
+        # it's possible for the importlib.machinery.FileFinder for
+        # a directory to have an outdated cache in the following situation:
+        # * a module in that directory is imported,
+        # * then a new module is created in that directory,
+        # * then that new module is imported.
+        #
+        # invalidate_cache() is used to prevent this.
+        #
+        # see https://docs.python.org/3/library/importlib.html
+        # sections #importlib.machinery.FileFinder and
+        # #importlib.invalidate_caches
         invalidate_caches()
 
     def tearDown(self):
