Facing error in OOPS program

class Stack:
def init(self):
self.items=()
def is_empty(self):
return self.items==()
def push(self,item):
self.items.append(item)
def pop(self):
self.items.pop()
def peek(self,i):
return self.items(len(self.items)-i-1)

def size(self):
    return len(self.items)
    

stack = Stack()
for c in "yesterday":
stack.push(c)

reversed_string = ""

for i in range(len(stack.items)):
reversed_string+=stack.peek(i)

print(reversed_string)