ob-python: Fix several issues with :session :results value

* lisp/ob-python.el (org-babel-python-evaluate-session): Fix a few
related issues with :session :results value blocks, including broken
if-else statements, indented blocks with blank lines, and returning
the wrong value when underscore has been used.
(org-babel-python--eval-ast): New constant variable, a string
consisting of Python code to execute a source block using ast.

Previously, python blocks with parameters ":session :results value"
were entered line-by-line into the Python session, which could cause
issues around indentation and new lines.  Now, such python blocks are
written to temp files, then the built-in ast python module is used to
parse and execute them, and to extract the last line separately to
return as a result.  Introduces a change in behavior, requiring that
the last line must be a top-level expression statement if its result
is to be saved (otherwise, the result is None).

1 files changed, 41 insertions, 27 deletions

diff --git a/lisp/ob-python.el b/lisp/ob-python.el
index 823f6e63d57..5f71577cb67 100644
--- a/lisp/ob-python.el
+++ b/lisp/ob-python.el
@@ -247,6 +247,25 @@ open('%s', 'w').write( pprint.pformat(main()) )")
    ")); "
    "__org_babel_python_fh.close()"))
 
+(defconst org-babel-python--eval-ast "\
+import ast
+try:
+    with open('%s') as f:
+        __org_babel_python_ast = ast.parse(f.read())
+    __org_babel_python_final = __org_babel_python_ast.body[-1]
+    if isinstance(__org_babel_python_final, ast.Expr):
+        __org_babel_python_ast.body = __org_babel_python_ast.body[:-1]
+        exec(compile(__org_babel_python_ast, '<string>', 'exec'))
+        __org_babel_python_final = eval(compile(ast.Expression(
+            __org_babel_python_final.value), '<string>', 'eval'))
+    else:
+        exec(compile(__org_babel_python_ast, '<string>', 'exec'))
+        __org_babel_python_final = None
+except Exception:
+    from traceback import format_exc
+    __org_babel_python_final = format_exc()
+    raise")
+
 (defun org-babel-python-evaluate
   (session body &optional result-type result-params preamble)
   "Evaluate BODY as Python code."
@@ -294,32 +313,9 @@ 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)))
-         (dump-last-value
-          (lambda
-            (tmp-file pp)
-            (mapc
-             (lambda (statement) (insert statement) (funcall send-wait))
-             (if pp
-                 (list
-                  "import pprint"
-                  (format "open('%s', 'w').write(pprint.pformat(_))"
-                          (org-babel-process-file-name tmp-file 'noquote)))
-               (list (format "open('%s', 'w').write(str(_))"
-                             (org-babel-process-file-name tmp-file
-                                                          'noquote)))))))
          (last-indent 0)
          (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))
-                                 (setq last-indent curr-indent))
-                             (setq last-indent 0)))
                          (insert line)
                          (funcall send-wait))
                        (funcall send-wait)))
@@ -344,17 +340,35 @@ last statement in BODY, as elisp."
                    (funcall send-wait))
                  2) "\n")))
             (`value
-             (let ((tmp-file (org-babel-temp-file "python-")))
+             (let ((tmp-results-file (org-babel-temp-file "python-"))
+                   (body (let ((tmp-src-file (org-babel-temp-file
+                                              "python-")))
+                           (with-temp-file tmp-src-file (insert body))
+                           (format org-babel-python--eval-ast
+                                   tmp-src-file))))
                (org-babel-comint-with-output
                    (session org-babel-python-eoe-indicator nil body)
                  (let ((comint-process-echoes nil))
                    (funcall input-body body)
-                   (funcall dump-last-value tmp-file
-                            (member "pp" result-params))
+                   (dolist
+                       (statement
+                        (if (member "pp" result-params)
+                            (list
+                             "import pprint"
+                             (format "open('%s', 'w').write(pprint.pformat(\
+__org_babel_python_final))"
+                                     (org-babel-process-file-name
+                                      tmp-results-file 'noquote)))
+                          (list (format "open('%s', 'w').write(str(\
+__org_babel_python_final))"
+                                        (org-babel-process-file-name
+                                         tmp-results-file 'noquote)))))
+                     (insert statement)
+                     (funcall send-wait))
                    (funcall send-wait) (funcall send-wait)
                    (insert org-babel-python-eoe-indicator)
                    (funcall send-wait)))
-               (org-babel-eval-read-file tmp-file))))))
+               (org-babel-eval-read-file tmp-results-file))))))
     (unless (string= (substring org-babel-python-eoe-indicator 1 -1) results)
       (org-babel-result-cond result-params
         results