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, 35 insertions, 0 deletions

diff --git a/testing/lisp/test-ob-python.el b/testing/lisp/test-ob-python.el
index 48ca3d64088..7e2826404f2 100644
--- a/testing/lisp/test-ob-python.el
+++ b/testing/lisp/test-ob-python.el
@@ -138,6 +138,41 @@ if True:
               (org-babel-execute-maybe)
               (org-babel-execute-src-block)))))
 
+(ert-deftest test-ob-python/if-else-block ()
+  (should
+   (equal "success" (org-test-with-temp-text "#+begin_src python :session :results value
+value = 'failure'
+if False:
+    pass
+else:
+    value = 'success'
+value
+#+end_src"
+              (org-babel-execute-src-block)))))
+
+(ert-deftest test-ob-python/indent-block-with-blank-lines ()
+  (should
+   (equal 20
+          (org-test-with-temp-text "#+begin_src python :session :results value
+  foo = 0
+  for i in range(10):
+      foo += 1
+
+      foo += 1
+
+  foo
+#+end_src"
+            (org-babel-execute-src-block)))))
+
+(ert-deftest test-ob-python/assign-underscore ()
+  (should
+   (equal "success"
+          (org-test-with-temp-text "#+begin_src python :session :results value
+_ = 'failure'
+'success'
+#+end_src"
+            (org-babel-execute-src-block)))))
+
 (provide 'test-ob-python)
 
 ;;; test-ob-python.el ends here