* 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).
cc89d5523f