python常见报错

arr=[1,2,3,3,4]
a="".join(arr)
print(a)

arr=[1,2,3,3,4]
arr=map(str,arr)
a="".join(arr)
print(a)

matrix=[[1,2,3],[4,5,6],[7,8,9]]
print (matrix)
matrix90=list(zip(*matrix))
print (matrix90)

matrix=[[1,2,3],[4,5,6],[7,8,9]]
print (matrix)
matrix90=list(zip(*matrix))
matrix90=[list(i) for i in matrix90 ]
print (matrix90)

s="abs"
n=len(s)
s=sorted(s)
visited=[False for _ in range(n)]
ans=[]
def dfs(ss):
    if len(ss)==n:
        ans.append(ss)
        return
    for i in range(n):
        if i>0 and s[i-1]==s[i] and not visited[i-1]:
            continue
        if not visited[i]:
            visited[i]=True
            dfs(ss+s[i])
            visited[i]=False
    return
dfs('')
print(ans)

from itertools import permutations
s="abs"
print (list(set("".join(list(i)) for i in permutations(s))))

rows=2
cols=7
visited = [[False] *cols] *rows
print(visited)
visited[0][0]=True
print(visited)

rows=2
cols=7
visited = [[False] *cols] *rows
print(id(visited[0]))
print(id(visited[1]))

rows=2
cols=7
visited = [[False] *cols for _ in range(rows)]
print(id(visited[0]))
print(id(visited[1]))