Anything that interferes with that - such as python format-strings -
has to take a back seat, regardless of its perceived benefits.
+**If you absolutely must** use python-format-strings, **only** do
+so by restricting to variables. Create temporary variables if you
+have to.
+
+ y = '/'.join(a_list)
+ x = f"{y}"
+
### PEP8 format
* all code needs to conform to pep8. use either pep8checker or better