Cleaner fix for qt execute_file bug:

Possible because double quotes can be escaped in double quotes (unlike single in single) in posix.

IPython/frontend/qt/console/ipython_widget.py

@@ -277,18 +277,13 b' class IPythonWidget(FrontendWidget):'
 
         # Perhaps we should not be using %run directly, but while we
         # are, it is necessary to quote or escape filenames containing spaces 
-        # or quotes. As much as possible, we quote: more readable than escape.
-        if '"' in path:
+        # or quotes. Note that in this context, because run uses posix
+        # parsing, we can escape double quotes in a double quoted filename,
+        # but can't escape singe quotes in a single quoted filename.
             if "'" in path:
-                # In this case, because %run 'a\'b"c.py' fails, we must escape
-                # all quotes and spaces.
-                for c in '" \'':
-                    path = path.replace(c, '\\'+c)
-            else:
+            path = '"%s"' % path.replace('"', '\\"')
+        elif ' ' in path or '"' in path:
                 path = "'%s'" % path
-        elif ' ' in path or "'" in path:
-            path = '"%s"' % path
-
         self.execute('%%run %s' % path, hidden=hidden)
 
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