python program starting with unmatched quote spews spaces to stdout

Lib/test/test_cmd_line.py

 # Tests invocation of the interpreter with various command line arguments
 # Most tests are executed with environment variables ignored
 # See test_cmd_line_script.py for testing of script execution
 
 import test.support, unittest
 import os
 import sys
 import subprocess
 import tempfile
 from test.script_helper import spawn_python, kill_python, assert_python_ok, assert_python_failure
@@ skipping 240 matching lines @@
         # on Windows (sys.stdin is opened in binary mode)
         self.check_input(
             "import sys; print(repr(sys.stdin.readline()))",
             b"'abc\\n'")
 
     def test_builtin_input(self):
         # Issue #11272: check that input() strips newlines ('\n' or '\r\n')
         self.check_input(
             "print(repr(input()))",
             b"'abc'")
+
+    def test_unmached_quote(self):
+        # Issue #10206: python program starting with unmatched quote
+        # spews spaces to stdout
+        rc, out, err = assert_python_failure('-c', "'")
+        self.assertRegex(err.decode('ascii', 'ignore'), 'SyntaxError')
+        self.assertEqual(b'', out) 
 
 
 def test_main():
     test.support.run_unittest(CmdLineTest)
     test.support.reap_children()
 
 if __name__ == "__main__":
     test_main()