Diagonal traversal of binary tree

def diagonal(root):
    q=deque()
    q.append(root)
    ans=[]
    while q:
        for _ in range(len(q)):
            t=q.popleft()
            ans.append(t.data)
            while t:
                if t.left:q.append(t.left)
                t=t.right
                if t:ans.append(t.data)
    return ans