Update pop function

data_structures/stacks/stack.py

@@ -4,6 +4,8 @@
 class StackOverflowError(BaseException):
     pass
 
+class StackUnderflowError(BaseException):
+    pass
 
 class Stack:
     """A stack is an abstract data type that serves as a collection of
@@ -32,6 +34,8 @@ def push(self, data):
 
     def pop(self):
         """Pop an element off of the top of the stack."""
+        if not self.stack: # Condition to check Underflow of stack
+            pass        
         return self.stack.pop()
 
     def peek(self):
@@ -64,6 +68,7 @@ def test_stack() -> None:
     assert stack.is_full() is False
     assert str(stack) == "[]"
 
+
     try:
         _ = stack.pop()
         assert False  # This should not happen