The following python code uses only whitespaces for the different indentdation levels:
a_list = ['elem1', 'elem2', 'elem3'] for elem in a_list: print(elem) for char in elem: print char I enter this code into a SRC block with #+BEGIN_SRC python :tangle blank_test.py #+END_SRC by pressing C-' inside the block (which opens the editing buffer python-mode). Then I press C-' again, after which I tangle the code to blank_test.py by pressing C-u C-c C-v C-t. The resulting file blank_test.py will contain a mix of tabs and spaces for the different intendation levels. (I checked this with whitespace.el). Above behaviour is a bug, since Python3 forbids mixing of spaces and tabs. (Python2 is more relaxed about mixing of tabs and spaces). Thus, the above code, syntactical correctly entered into an OrgSrc buffer, will result in code that can not be run in python3 when tangled from an org-mode file. Emacs : GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.5) of 2017-09-12 on hullmann, modified by Debian Package: Org mode version 9.1.4 (9.1.4-dist @ /home/ehere/emacs-scripts/org-9.1.4/lisp/)