i want to know that code. When I entered "def dfs$($A$)$:

visited $=[]$

answer $=[]$

stack $=[0]$

while stack:

node $=$ stack$-$pop$()$

if node not in visited: visited. append $($node$)$

answer. append $($node$)$

stack.extend$($A$[$node$]-$ set$($visited$))$

return answer" in the second code, an error like "Exception has occurred: AssertionError

exception: no description

line $76,$ in

assert dfs$\_$result $==[0,1,4,5,2,6,3]$

AssertionError: $"$ appeared.