Emacs Org Mode: Executing simple python code

Question

How can I execute very simple Python-Code in Emacs' Org Mode?

The first example works fine, however I can't make it give me the result of simplest computations:

; works
#+begin_src python
def foo(x):
  if x>0:
    return x+10

  else:
    return x-1

return foo(50)
#+end_src

#+RESULTS:
: 60

; does not work
#+begin_src python
1+1
#+end_src

#+RESULTS:
: None

; does not work
#+begin_src python
print(1+1)
#+end_src

#+RESULTS:
: None

I set up Org Mode using the following lines:

;; enable python for in-buffer evaluation
(org-babel-do-load-languages
 'org-babel-load-languages
 '((python . t)))

;; all python code be safe
(defun my-org-confirm-babel-evaluate (lang body)
(not (string= lang "python")))
(setq org-confirm-babel-evaluate 'my-org-confirm-babel-evaluate)

Answer 1

There are two ways of getting the result of a source block - output and value. You mixed them up, hence the troubles.

First block is fine.

To fix the second block:

#+begin_src python :results value
return 1+1
#+end_src

To fix the third block:

#+begin_src python :results output
print 1+1
#+end_src

When output mode is value you must return. Just putting it there like you did with 1+1 won't do. In the third one you want the result to be printed output, but your default session setting is value(mine defaults to output btw).

And this bit about org-confirm-babel-evaluate is kind of irrelevant to the question. I just have it set to nil.

Answer 2

You may still face problems like blank lines cause error in function definition. The solution is given in original thread. I also posted below

(setq org-babel-python-command "ipython3 --no-banner --classic --no-confirm-exit")

;; use %cpaste to paste code into ipython in org mode
(defadvice org-babel-python-evaluate-session
(around org-python-use-cpaste
        (session body &optional result-type result-params) activate)
        "Add a %cpaste and '--' to the body, so that ipython does the right thing."
(setq body (concat "%cpaste\n" body "\n--"))
ad-do-it
(if (stringp ad-return-value)
  (setq ad-return-value (replace-regexp-in-string "\\(^Pasting code; enter '--' alone on the line to stop or use Ctrl-D\.[\r\n]:*\\)" "" ad-return-value))))