```
class Solution(object):
def isValidSudoku(self, board):
"""
:type board: List[List[str]]
:rtype: bool
"""
rows = {}
columns = {}
squares = {}
# can be done with defaultdict as well:
for n in range(9):
rows[n] = set()
columns[n] = set()
squares[n] = set()
for r in range(9):
for c in range(9):
num = board[r][c]
if num == '.':
continue
s = (r/3)*3 + c/3
if num in rows[r] or num in columns[c] or num in squares[s]:
return False
rows[r].add(num)
columns[c].add(num)
squares[s].add(num)
return True
```

My question is if there is any other syntax to initialize multiple variables to empty dictionaries? I tried the multiple equal sign syntax `rows = columns = squares = {}`

, but it appears that this just creates one dictionary that can be referenced by three names. I was having trouble because `rows[r].add(num)`

was also performing `columns[r].add(num)`

and `squares[r].add(num)`

. Also in the for loop, I couldn't just do `rows[n] = columns[n] = squares[n] = set()`

either. The code behaved very weirdly when I did so. Can someone explain what the multiple equal sign syntax does exactly in this context?