ein-python: Fix for #252

EIN should properly handle indentation in the worksheet as it once did long ago.
Issues was that python mode no longer uses the global variables
`python-ident-levels' for tracking ident. Now we advise around
`python-indent--calculate-indentation'. This is an internal function so may not
be the best call, but it works.

If it breaks maybe take a look at advising `python-ident-calculate-indentation'.

lisp/ein-python.el

@@ -37,40 +37,45 @@
           "except" "finally" "for" "while" "with")
       symbol-end))
 
-(defun ein:python-indent-calculate-levels ()
-  "Forcefully set indent level to 0 when there is no python block
-yet in this cell."
-  (ein:and-let* ((cell (ein:worksheet-get-current-cell :noerror t))
-                 (beg (ein:cell-input-pos-min cell))
-                 ((< beg (point))))
-    (save-excursion
-      (unless (search-backward-regexp ein:python-block-start beg t)
-        (setq python-indent-levels (list 0))
-        (setq python-indent-current-level 0)
-        t))))
+(defun ein:python-indent-calculate-indentation--around (orig &rest args)
+  "False if there is no python block yet in this cell."
+  (condition-case _
+      (ein:and-let* ((cell (ein:worksheet-get-current-cell))
+                     (beg (ein:cell-input-pos-min cell))
+                     (p (point))
+                     ((< beg (point))))
+        (if (not (search-backward-regexp ein:python-block-start beg t))
+            0
+          (goto-char p)
+          (apply orig args)))
+    (error (apply orig args))))
 
-(defadvice python-indent-calculate-levels
-    (around ein:python-indent-calculate-levels activate)
-  "Hack `python-indent-calculate-levels' to reset indent per cell.
+(advice-add 'python-indent--calculate-indentation :around #'ein:python-indent-calculate-indentation--around)
 
-Let's say you have a notebook something like this::
+;; (defadvice python-indent-calculate-indentation
+;;     (around ein:python-indent-calculate-levels activate)
+;;   "Hack `python-indent-calculate-levels' to reset indent per cell.
 
-  In [1]:
-  def func():
-      pass
+;; Let's say you have a notebook something like this::
 
-  In [2]:
-  something[]
+;;   In [1]:
+;;   def func():
+;;       pass
 
-Here, ``[]`` is the cursor position.  When you hit the tab here,
-you don't expect it to indent.  However, python.el tries to follow
-the indent of ``func()`` then you get indentation.  This advice
-workaround this problem.
+;;   In [2]:
+;;   something[]
+
+;; Here, ``[]`` is the cursor position.  When you hit the tab here,
+;; you don't expect it to indent.  However, python.el tries to follow
+;; the indent of ``func()`` then you get indentation.  This advice
+;; workaround this problem.
+
+;; Note that this workaround does not work with the MuMaMo based
+;; notebook mode."
+;;   (if (ein:ein-block-start-p)
+;;       ad-do-it
+;;     0))
 
-Note that this workaround does not work with the MuMaMo based
-notebook mode."
-  (unless (ein:python-indent-calculate-levels)
-    ad-do-it))
 
 (provide 'ein-python)