Как проверить, находится ли элемент в массиве

class LL(object):
    def __init__(self,val):
        self.val = val
        self.next = None

    def pushNodeEnd(self,top,val):
        if top is None:
            top.val=val
            top.next=None
        else:
            tmp=top
            while (tmp.next != None):
                tmp=tmp.next        
            newNode=LL(val)
            newNode.next=None
            tmp.next=newNode

    def pushNodeFront(self,top,val):
        if top is None:
            top.val=val
            top.next=None
        else:
            newNode=LL(val)
            newNode.next=top
            top=newNode

    def popNodeFront(self,top):
        if top is None:
            return
        else:
            sav=top
            top=top.next
        return sav

    def popNodeEnd(self,top):
        if top is None:
            return
        else:
            tmp=top
            while (tmp.next != None):
                prev=tmp
                tmp=tmp.next
            prev.next=None
        return tmp

top=LL(10)
top.pushNodeEnd(top, 20)
top.pushNodeEnd(top, 30)
pop=top.popNodeEnd(top)
print (pop.val)