ob-python: Fix session blocks not waiting for value result

* lisp/ob-python.el (py-shell-send-string): Remove unneeded
declare-function.
(org-babel-python-eoe-indicator): Add back this const.
(org-babel-python--eval-ast): Fix spacing so the block can be entered
line by line into the interpreter.
(org-babel-python-evaluate-session): Revert previous changes to
evaluation for value results.
* testing/lisp/test-ob-python.el (test-ob-python/session-value-sleep):
New test for session blocks that don't return immediately.

632ceabb1 introduced a bug where session blocks don't wait for value
results if not returned immediately.  This reverts part of that
commit, specifically for evaluation of session blocks with value
results.  It leaves other parts of that commit alone, for example the
changes to session output results, which is more robust handling
prompts from ipython interpreter.

A downside of reverting the session value implementation is that the
ugly code from org-babel-python--eval-ast is again printed in the
console, but this is less bad than the new bug that was introduced by
the change, hence reverted.

lisp/ob-python.el

@@ -33,7 +33,6 @@
 
 (declare-function py-shell "ext:python-mode" (&rest args))
 (declare-function py-toggle-shells "ext:python-mode" (arg))
-(declare-function py-shell-send-string "ext:python-mode" (strg &optional process))
 (declare-function py-send-string-no-output "ext:python-mode" (strg &optional process buffer-name))
 
 (defvar org-babel-tangle-lang-exts)
@@ -225,6 +224,9 @@ then create.  Return the initialized session."
     (org-babel-python-session-buffer
      (org-babel-python-initiate-session-by-key session))))
 
+(defvar org-babel-python-eoe-indicator "'org_babel_python_eoe'"
+  "A string to indicate that evaluation has completed.")
+
 (defconst org-babel-python-wrapper-method
   "
 def main():
@@ -249,9 +251,9 @@ to evaluate.")
 
 (defconst org-babel-python--eval-ast "\
 import ast
-
 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):
@@ -326,13 +328,18 @@ last statement in BODY, as elisp."
 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."
-  (require org-babel-python-mode)
   (let* ((python-shell-buffer-name (org-babel-python-without-earmuffs session))
+	 (send-wait (lambda () (comint-send-input nil t) (sleep-for 0 5)))
+	 (input-body (lambda (body)
+		       (dolist (line (split-string body "[\r\n]"))
+			 (insert line)
+			 (funcall send-wait))
+		       (funcall send-wait)))
 	 (tmp-src-file (org-babel-temp-file "python-"))
-	 (results
+         (results
 	  (progn
 	    (with-temp-file tmp-src-file (insert body))
-	    (pcase result-type
+            (pcase result-type
 	      (`output
 	       (let ((src-str (format org-babel-python--exec-tmpfile
 				      (org-babel-process-file-name
@@ -341,21 +348,27 @@ last statement in BODY, as elisp."
 		     (py-send-string-no-output
 		      src-str (get-buffer-process session) session)
 		   (python-shell-send-string-no-output src-str))))
-	      (`value
-	       (let* ((results-file (org-babel-temp-file "python-"))
-		      (src-str (format
-				org-babel-python--eval-ast
-				(org-babel-process-file-name tmp-src-file 'noquote)
-				(org-babel-process-file-name results-file 'noquote)
-				(org-babel-python-var-to-python result-params))))
-		 (if (eq 'python-mode org-babel-python-mode)
-		     (py-shell-send-string src-str (get-buffer-process session))
-		   (python-shell-send-string src-str))
-		 (sleep-for 0 5)
-		 (org-babel-eval-read-file results-file)))))))
-    (org-babel-result-cond result-params
-      results
-      (org-babel-python-table-or-string results))))
+              (`value
+               (let* ((tmp-results-file (org-babel-temp-file "python-"))
+		      (body (format org-babel-python--eval-ast
+				    (org-babel-process-file-name
+				     tmp-src-file 'noquote)
+				    (org-babel-process-file-name
+				     tmp-results-file 'noquote)
+				    (if (member "pp" result-params)
+					"True" "False"))))
+		 (org-babel-comint-with-output
+                     (session org-babel-python-eoe-indicator nil body)
+                   (let ((comint-process-echoes nil))
+                     (funcall input-body body)
+                     (funcall send-wait) (funcall send-wait)
+                     (insert org-babel-python-eoe-indicator)
+                     (funcall send-wait)))
+		 (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
+        (org-babel-python-table-or-string results)))))
 
 (defun org-babel-python-read-string (string)
   "Strip \\='s from around Python string."

testing/lisp/test-ob-python.el

@@ -200,6 +200,16 @@ return text
 #+end_src"
 	    (org-babel-execute-src-block)))))
 
+(ert-deftest test-ob-python/session-value-sleep ()
+  (should
+   (equal "success"
+	  (org-test-with-temp-text "#+begin_src python :session :results value
+import time
+time.sleep(.1)
+'success'
+#+end_src"
+	    (org-babel-execute-src-block)))))
+
 (provide 'test-ob-python)
 
 ;;; test-ob-python.el ends here