Subtract feature

src/service/calculation_service.py

@@ -1,6 +1,7 @@
 """Module for the CalculationService class"""
 from tkinter import StringVar
 import divide_service as divide_service
+import subtract_service as subtract_service
 
 
 class CalculationService:
@@ -29,10 +30,12 @@ def equalpress(self):
         try:
 
             # evaluate the expression/calculation
-            if "/" not in self.expression:
-                total = str(eval(self.expression))
-            else:
+            if "/" in self.expression:
                 total = str(divide_service.divide(self.expression))
+            if "-" in self.expression:
+                total = str(subtract_service.subtract(self.expression))
+            else:
+                total = str(eval(self.expression))
 
             if float(total) > 10:
                 total = total + " <:o)"

src/service/subtract_service.py

@@ -0,0 +1,6 @@
+
+
+def add(string):
+    arguments = string.split("-")
+    result = int(arguments[0]) - int(arguments[1])
+    return result