Merge pull request #5 from maddypie/refactoring

Refactoring done 🏆

README.md

@@ -7,10 +7,10 @@ Currently the program supports 'Addition :heavy_plus_sign:', 'Subtraction :heavy
 
 #### User interface of PyCalc *v0.1-beta* :desktop_computer:
 
-![As of v0.1-alpha](https://github.com/maddypie/PyCalc/blob/master/PyCalcDemo.png)
+![As of v0.1-beta](https://github.com/maddypie/PyCalc/blob/master/PyCalcDemo.png)
 
 #### Tasks List :writing_hand:
-- [ ] **Refactor source.py**
+- [x] **Refactor source.py**
 - [x] Add 'Copy' functionality, to copy the result. Currently 'Copy' button does not do anything.
 - [x] Bind 'Number-pad' keys to enter input.
 - [ ] Option to switch between 'Simple' to 'Advanced' mode. Advanced mode should have more funtionalities.

core_logic.py

@@ -0,0 +1,36 @@
+class Calculate():
+    ans: str
+    _get_value = {
+            '/': lambda x, y: x/y,
+            '*': lambda x, y: x*y,
+            '+': lambda x, y: x+y,
+            '-': lambda x, y: x-y
+            }
+
+    def __init__(self, expr_as_list, operators):
+        self.expr_as_list = expr_as_list
+        self.operators = operators
+
+    def calculate(self) -> str:
+        while self.operators[0] in self.expr_as_list:
+            index = self.expr_as_list.index(self.operators[0])
+            self.__partial_calculate(index)
+        while self.operators[1] in self.expr_as_list:
+            index = self.expr_as_list.index(self.operators[1])
+            self.__partial_calculate(index)
+        while self.operators[2] in self.expr_as_list:
+            index = self.expr_as_list.index(self.operators[2])
+            self.__partial_calculate(index)
+        while self.operators[3] in self.expr_as_list:
+            index = self.expr_as_list.index(self.operators[3])
+            self.__partial_calculate(index)
+        self.ans = self.expr_as_list[0]
+        return self.ans
+
+    def __partial_calculate(self, index) -> None:
+        operator = self.expr_as_list[index]
+        left_operand = float(self.expr_as_list[index-1])
+        right_operand = float(self.expr_as_list[index+1])
+        sub_result = self._get_value[operator](left_operand, right_operand)
+        self.expr_as_list[index-1:index+2] = [str(sub_result)]
+