Upload calculator.py

src/calculator.py

+
+def add(x,y):
+    return x+y
+
+def substract(x,y):
+    return x-y
+
+def multiply(x,y):
+    return x*y
+
+def divide(x,y):
+    if y == 0:
+        raise ValueError('Can not divide by zero!')
+    return x/y