stack.py now passes unittests. added missing parentheses in conditional in method __precedence()

Signed-off-by: IanDoarn <[email protected]>

Author: IanDoarn

pygorithm/data_structures/stack.py

@@ -116,6 +116,7 @@ def infix_to_postfix(self):
         function to generate postfix expression from infix expression
         """
         postfix = []
+
         for i in range(len(self.expression)):
             if self._is_operand(self.expression[i]):
                 postfix.append(self.expression[i])