Change fragile code to pretty-print using black instead of pprint

README.org

@@ -2172,7 +2172,9 @@ list detailing and motivating each listing:
    and it provides a function to remove the indentation of all =org-src-mode=
    blocks without =-i= switch.
 7. Listing [[lst:setup-ob-python]] allows to pretty-print Python session source
-   block values with [[https://github.com/psf/black#readme][black]] instead of [[https://docs.python.org/3/library/pprint.html][pprint]].
+   block values with [[https://github.com/psf/black#readme][black]] instead of [[https://docs.python.org/3/library/pprint.html][pprint]].  This snippet may break in the
+   future, because it sets =org-babel-python--def-format-value= which is a
+   constant declared "private" by two dashes in its name!
 8. Listing [[lst:set-org-export-options]] selects the =non-intrusive= expert user
    interface for export dispatching.
 9. Listing [[lst:setup-org-for-lualatex-export]] and
@@ -2382,42 +2384,53 @@ When called twice, replace the previously inserted \\(\\) by one $."
 #+end_src
 
 #+caption[Setup =ob-python=]:
-#+caption: Setup =ob-python=.
+#+caption: Setup =ob-python=.  This snippet may break in the future!
 #+name: lst:setup-ob-python
 #+begin_src emacs-lisp -n :results silent
 (with-eval-after-load 'ob-python
-  (defun org-babel-python-format-session-value-override
+  (setq org-babel-python--def-format-value "\
-      (src-file result-file result-params)
+def __org_babel_python_format_value(result, result_file, result_params):
-    "Return Python code to evaluate SRC-FILE and write result to RESULT-FILE.
+    with open(result_file, 'w') as f:
-Use `black' instead of `pprint' when \"pp\" is a member of RESULT-PARAMS."
+        if 'graphics' in result_params:
-    (format "\
+            result.savefig(result_file)
-import ast
+        elif 'pp' in result_params:
-with open('%s') as __org_babel_python_tmpfile:
-    __org_babel_python_ast = ast.parse(__org_babel_python_tmpfile.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')
-    )
-    with open('%s', 'w') as __org_babel_python_tmpfile:
-        if %s:
             import black
-            __org_babel_python_tmpfile.write(
+            f.write(black.format_str(repr(result), mode=black.Mode()))
-                black.format_str(repr(__org_babel_python_final), mode=black.Mode())
+        elif 'list' in result_params and isinstance(result, dict):
-            )
+            f.write(str(['{} :: {}'.format(k, v) for k, v in result.items()]))
         else:
-            __org_babel_python_tmpfile.write(str(__org_babel_python_final))
+            if not set(result_params).intersection(\
-else:
+['scalar', 'verbatim', 'raw']):
-    exec(compile(__org_babel_python_ast, '<string>', 'exec'))
+                def dict2table(res):
-    __org_babel_python_final = None"
+                    if isinstance(res, dict):
-            (org-babel-process-file-name src-file 'noquote)
+                        return [(k, dict2table(v)) for k, v in res.items()]
-            (org-babel-process-file-name result-file 'noquote)
+                    elif isinstance(res, list) or isinstance(res, tuple):
-            (if (member "pp" result-params) "True" "False")))
+                        return [dict2table(x) for x in res]
-
+                    else:
-  (advice-add 'org-babel-python-format-session-value
+                        return res
-              :override #'org-babel-python-format-session-value-override))
+                if 'table' in result_params:
+                    result = dict2table(result)
+                try:
+                    import pandas
+                except ImportError:
+                    pass
+                else:
+                    if isinstance(result, pandas.DataFrame) and 'table' in result_params:
+                        result = [[result.index.name or ''] + list(result.columns)] + \
+[None] + [[i] + list(row) for i, row in result.iterrows()]
+                    elif isinstance(result, pandas.Series) and 'table' in result_params:
+                        result = list(result.items())
+                try:
+                    import numpy
+                except ImportError:
+                    pass
+                else:
+                    if isinstance(result, numpy.ndarray):
+                        if 'table' in result_params:
+                            result = result.tolist()
+                        else:
+                            result = repr(result)
+            f.write(str(result))"))
 #+end_src
 
 #+caption[Set =org-export= options]: