python-swap-quotes.el

(defun python-swap-quotes ()
  (interactive)
  (save-excursion
    (let ((state (syntax-ppss)))
      (when (eq 'string (syntax-ppss-context state))
        (let* ((left (nth 8 state))
               (right (1- (scan-sexps left 1)))
               (newquote (if (= ?' (char-after left))
                             ?\" ?')))
          (dolist (loc (list left right))
            (goto-char loc)
            (delete-char 1)
            (insert-char newquote 1)))))))

(add-hook 'python-mode-hook (lambda ()
                          (local-unset-key "\C-c\C-s")
                          (local-set-key "\C-c\C-s"
                                         'python-swap-quotes)))