Depth-first search python

` ````
def dfs(graph, vertex):
output = []
if isinstance(graph, dict):
visited = {key: False for key in graph.keys()}
if isinstance(graph, list):
visited = [False] * len(graph)
stack = []
stack.append(vertex)
while stack:
v = stack.pop()
if not visited[v]:
visited[v] = True
output.append(v)
for neighbor in graph[v]:
stack.append(neighbor)
return output
```