variable "x" in block "square" must be assigned a default value

I am using Emacs 24/Org 7.8 and am having some issues with org-babel. I want to call a block of code with #+call:

#+name: square(x)
#+begin_src python
return x*x
#+end_src
#+call: square(x=6)

Evaluating #+call with C-c C-c gives the message:

variable "x" in block "square" must be assigned a default value

Any advice on how to debug this? I have the following code related org-babel in my init.el:

(org-babel-do-load-languages
     'org-babel-load-languages
     '((R . t)
       (python . t)
       (js . t)
       (scheme . t)
       (C . t)
       (lilypond . t)
       (maxima . t)
       (octave . t)))

Adding :var x=1 to the begin_src line like so:

#+name: square(x)
#+begin_src python :var x=1
return x*x
#+end_src
#+call: square(x=6)

don't stop me from receiving the error.

Investigating with the emacs debugger, I find that ref isn't holding "x=6", but is instead holding "x".

 (org-babel-merge-params
             (mapcar
              (lambda (ref) (cons :var ref))
              (mapcar
               (lambda (var) ;; check that each variable is initialized
         (if (string-match ".+=.+" var)
                 var
               (error
                "variable \"%s\"%s must be assigned a default value"
                var (if name (format " in block \"%s\"" name) ""))))
               (org-babel-ref-split-args (match-string 5))))
             (nth 2 info))

Solution

Treating your questions as two parts (issue with variable X and issue with emacs-lisp).

Emacs-Lisp

I would suggest making sure you include (emacs-lisp . t) in your list of org-babel-load-languages. That should resolve the issue with it not finding emacs-lisp. You can also try M-: (require 'ob-emacs-lisp) and your issue should be resolved (it forces it to load the emacs-lisp babel code).

Variable Issue

I had to do a few tests to figure out exactly where the issue was, it turns out there's two ways to declare variables when trying to run Org Babel blocks. I'm using emacs-lisp for the test because I don't have a python interpreter installed at the moment, but the results should be equivalent. The error message is telling you that you must by default declare a value for your variable (x=1). Once you do that your code blocks should be fine.

* Declare variable in name
#+name: square(x=1)
#+begin_src emacs-lisp
  (* x x)
#+end_src

#+results: square
: 1

#+call: square(x=45)

#+results: square(x=45)
: 2025

#+call: square(5)

#+results: square(5)
: 25

* Declare variable in begin_src
#+name: square2
#+begin_src emacs-lisp :var x=1
  (* x x)
#+end_src

#+results: square2
: 1

#+call: square2(5)

#+results: square2(5)
: 25

#+call: square2(x=45)

#+results: square2(x=45)
: 2025