In the following org-mode source snippet, no result is generated:
#+BEGIN_SRC ipython :session
import numpy as np
#+END_SRC
However, upon execution #+RESULTS: is added to the document. How can I configure org-mode / babel to only insert results when there is something to display?
I know I can disable output using :results silent, but I'd prefer not to have to specify a different flag depending on whether a result is generated or not.
Using ob-ipython with Org 9, I got this to work with the following hack, provided that source blocks are configured to return values (i.e., the default header specifies :results value):
; don't label empty outputs, exclude empty result blocks
(advice-add 'ob-ipython--process-response :filter-return
(λ (contents)
(if (string-match-p "\\`# Out\[[0-9]+\]:\n\\'" contents)
"" contents)))
(advice-add 'org-babel-insert-result :filter-args
(λ (args)
(let ((result (car args))
(result-params (cadr args))
(others (cddr args)))
(apply 'list
result
(if (string-empty-p result) '("silent") result-params)
others))))
The first advice strips the output tag inserted by ob-ipython when there is nothing further in the output (making the result empty), while the second advice effectively applies :results silent when the result is empty. These pieces could be arranged differently depending on your use case.