Simple calculator with GUI

Features:

• additional buffer display on the top of the calculator
• repeating last action by clicking "=" (e.g. "2+2===" equals eight)
• chaining operations, one after another without need to click "=" each time (e.g. "2+6/2=" (This is the order of the pressed keys) equals four)
• changing operator after clicking another one (e.g. "6+-/3=" equals 2)
• creating negative numbers (if you're typing it as a first number too)
• clearing entry (CE)
• reseting calculator (C)
• adding comma
• sanitized entry
• buffer for last number above an entry

It was one of the first python projects