Added a "square" operand

calculator_tree.py

@@ -4,6 +4,7 @@ class Node:
         "-": (lambda x, y: x - y),
         "*": (lambda x, y: x * y),
         "/": (lambda x, y: x / y),
+        "^": (lambda x, y: x ** y),
     }
 
     def __init__(self, operator=None, value=None):
@@ -61,7 +62,7 @@ def extract_number(string):
     for ind, letter in enumerate(string):
         if letter.isdigit():
             result += letter
-        elif ind == 0 and letter in "+-*/":
+        elif ind == 0 and letter in Node.ops.keys():
             operator = letter
         else:
             break
@@ -88,7 +89,7 @@ def calculate(expr, binary_tree=None):
         binary_tree.root.add_right(new_number)
         root_node = binary_tree.root
     else:
-        if operator not in "*/":
+        if operator not in "*/^":
             binary_tree.add_root(Node(operator=operator), "left")
             binary_tree.root.add_right(new_number)
             root_node = binary_tree.root

test_calculator_tree.py

@@ -88,6 +88,31 @@ class TreeTestCalculateFunction(unittest.TestCase):
         res = calculate(expression)
         self.assertEqual(res.calculate_below(), 32)
 
+    def test_sqr(self):
+        """
+        Testing the the calculable result for expression '3^2'
+        """
+        expression = "3^2"
+        res = calculate(expression)
+        self.assertEqual(res.calculate_below(), 9)
+
+    def test_sqr_negative(self):
+        """
+        Testing the the calculable result for expression '-3^2'
+        """
+        expression = "-3^2"
+        res = calculate(expression)
+        self.assertEqual(res.calculate_below(), -9)
+
+    def test_sqr_subtraction(self):
+        """
+        Testing the the calculable result for expression '10-3^2'
+        """
+        expression = "10-3^2"
+        res = calculate(expression)
+        self.assertEqual(res.operator, "-")
+        self.assertEqual(res.calculate_below(), 1)
+
 
 if __name__ == '__main__':
     unittest.main()