src python in org-mode: IndentationError: unexpected indent

Question

mac 10.13.4 / emacs 25.3 (9.0) / org-version 9.1.12 / python 3.5.2

I am trying to understand why C-c C-c generate an IndentationError: unexpected indent when executing a simple code like the example below as a code block:

#+BEGIN_SRC python :session :exports results
  def spam():
      try:
          a, b = 1, 2    
      except:
          a, b = 11, 12
      finally:
          a = 'voila'
#+END_SRC

my init.el is as follows:

    ;; Set org mode
    (eval-after-load "org"
      '(org-babel-do-load-languages
        'org-babel-load-languages
        '((sh . t)
          (python . t)
          (emacs-lisp . t)
          (ditaa . t)
          ))
      )
    (setq org-src-tab-acts-natively t)

I have actually written this python code in a python buffer (C-c') and it works everywhere else except in the org-mode. I would really appreciate any lead

Answer 1

What's happening is that org-babel-python-evaluate-session sends an extra newline when the indentation level goes down, this causes the interpreter to close out the top-level block.

What I've done is just commented out that bit (forgive the wonky indentation, my file as received from elpa mixes tabs and spaces)

ob-python.el

(defun org-babel-python-evaluate-session
    (session body &optional result-type result-params)
  "Pass BODY to the Python process in SESSION.
If RESULT-TYPE equals `output' then return standard output as a
string.  If RESULT-TYPE equals `value' then return the value of the
last statement in BODY, as elisp."
  (let* ((send-wait (lambda () (comint-send-input nil t) (sleep-for 0 5)))
     ...
     (input-body (lambda (body)
       (dolist (line (split-string body "[\r\n]"))
             ;; Insert a blank line to end an indent
             ;; block.
             (let ((curr-indent (string-match "\\S-" line)))
               (if curr-indent
                   (progn
                 (when (< curr-indent last-indent)
                   (insert "")
                   ;(funcall send-wait) <- comment this out
                   ) ; move the closing paren to the next line
                 ...

The result is that top-level blocks are sent as one unit which may have implications if you're evaluating a large block (e.g. a god class). I haven't tested it extensively but it's been working for me.

Hope that helps.