NQueens problem not stopping after finding one solution

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The following is my code for the NQueens problem which is not stopping after finding one solution (I’ve placed a return after queen placed== queen placed so far) “qp==qpsf” return but its not stopping further recursive calls, could you help me resolved this issue and help me understand whats the cause for further calls of recursion even after returning at a point?

def NQueens(board,row,col,tq,qpsf,ans):

if(qpsf==tq):

    print(ans)

    return

if(col==len(board[0])):

    col=0

    row+=1

if(row==len(board)):

    return

if(isSafe(board,row,col)):

    board[row][col]=True

    NQueens(board,row,col+1,tq,qpsf+1,ans+"["+ str(row) + "," + str(col)+"]" )

    board[row][col]=False

NQueens(board,row,col+1,tq,qpsf,ans)

def isSafe(board,row,col):

#vertically up

r=row-1

c=col

while(r>=0):

    if board[r][c]==1:

        return False

    r-=1

#horizontally Left

r=row

c=col-1

while(c>=0):

    if board[r][c]==1:

        return False

    c-=1

#diagonally left

r=row-1

c=col-1

while(c>=0 and r>=0):

    if board[r][c]==1:

        return False

    c-=1

    r-=1

#diagonally right

r=row-1

c=col+1

while(c<len(board[0]) and r>=0):

    if board[r][c]==1:

        return False

    c+=1

    r-=1

return True

def backtrack(n):

board=[[False for i in range(n)]for j in range(n)]

NQueens(board,0,0,n,0,'')

backtrack(4)