Issue #19398: Extra slash no longer added to sys.path components in case of

empty compile-time PYTHONPATH components.  This fixes some tests in -S or -I
modes.

Lib/test/test_trace.py

@@ -311,11 +311,11 @@ class TestCoverage(unittest.TestCase):
         with captured_stdout() as stdout:
             self._coverage(tracer)
         stdout = stdout.getvalue()
-        self.assertTrue("pprint.py" in stdout)
-        self.assertTrue("case.py" in stdout)   # from unittest
+        self.assertIn("pprint.py", stdout)
+        self.assertIn("case.py", stdout)   # from unittest
         files = os.listdir(TESTFN)
-        self.assertTrue("pprint.cover" in files)
-        self.assertTrue("unittest.case.cover" in files)
+        self.assertIn("pprint.cover", files)
+        self.assertIn("unittest.case.cover", files)
 
     def test_coverage_ignore(self):
         # Ignore all files, nothing should be traced nor printed

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.7.0 alpha 1
 Core and Builtins
 -----------------
 
+- Issue #19398: Extra slash no longer added to sys.path components in case of
+  empty compile-time PYTHONPATH components.
+
 - Issue #28621: Sped up converting int to float by reusing faster bits counting
   implementation.  Patch by Adrian Wielgosik.
 

Modules/getpath.c

@@ -762,7 +762,10 @@ calculate_path(void)
 
         if (defpath[0] != SEP) {
             wcscat(buf, prefix);
-            wcscat(buf, separator);
+            if (prefixsz >= 2 && prefix[prefixsz - 2] != SEP &&
+                defpath[0] != (delim ? DELIM : L'\0')) {  /* not empty */
+                wcscat(buf, separator);
+            }
         }
 
         if (delim) {