Bind function key when in python-mode

Question

I want to bind f5 to launch pdb, but the minibuffer always says <f5> is undefined.

(use-package python-mode
  :bind (:map python-mode-map
          ("<[f5]>" . realgud:pdb))
  :config
  (load-library 'realgud))

Answer 1

Try this:

(use-package python-mode
  :bind (:map python-mode-map
          ([f5] . realgud:pdb)))

I can't see any reason why this would not work, but I should note that it's derived from my specific usage, which is slightly different.

I collect all my F-key bindings in an alist, directly calling bind-key on the car and cdr of each element. bind-key is what a :bind stanza in a use-package declaration expands to.

(defun ph/map-keys (key-mappings)
  "Bind keys using alist KEY-MAPPINGS."
  (dolist (key-mapping key-mappings)
    (let ((key-chord (car key-mapping)) (command (cdr key-mapping)))
      (when (and key-chord command (commandp command))
        (bind-key key-chord command)))))

The simple vector form [f5] works there for plain F-key bindings like ([f5] . my-command) (as suggested by @NickD in a comment above). Modifiers need slightly more complex syntax: ([(control f5)] . my-command).

Answer 2

If the goal is simply to bind a key in a given mode, use-package isn't the only road to Rome.

As long as the mode map variable is defined, define-key is also an option:

(define-key python-mode-map [f6] 'my-other-special-function)

If there is a need to test things out you might define an interactive function and use local-set-key.

;; Try invoking this once in python mode.
(defun bind-f5-in-python-mode ()
  (interactive)
  (local-set-key [f5] 'my-special-function))