Notes on LinkedList:

• The import is unused.
• It should allow creation of an empty list.
• Normally a linked list inserts items after the last item. Maybe I'm confused by the way insert works, but it looks like in your case head is always the last inserted entry in the list, and the list is traversed from head backwards through history using .next.
• delete should use search.

Notes on LinkedList:

• The import is unused.
• It should allow creation of an empty list.
• Normally a linked list inserts items after the last item. Maybe I'm confused by the way insert works, but it looks like in your case head is always the last inserted entry in the list, and the list is traversed from head backwards through history using .next.
• delete should use search.

Notes on Stack:

• self.data should be self.entries or something else descriptive.
• prnt should be as_string or even __str__.
• int(val) does not check whether something is an integer, it just tries to convert a value to an integer.
• +, -, * and / are arithmetic, not binary, operators.
• In Python 3 mathematical operators are modeled as functions.
• is_integer, is_binary_operator and postfixEval should not be part of Stack - they are not fundamental to the stack in any way.