Python:列表。remove()有线地

def get_variables(cells):
    domains = [1,2,3,4]
    variables = {}
    for cell in cells:
        if(cell == "C11"):
            variables[cell] = [1]
        elif(cell == "C22"):
            variables[cell] = [2]
        elif(cell == "C33"):
            variables[cell] = [3]
        elif(cell == "C44"):
            variables[cell] = [4]
        else:
            variables[cell] = domains

cells = ['C'+x+y for x in "1234" for y in "1234"]
variables = get_variables(cells)
csp = CSP(variables, constraints, assigned)
pprint(csp.variables)
csp.variables["C12"].remove(1)
print(csp.variables["C13"])

output: 
{'C11': [1],
 'C12': [1, 2, 3, 4],
 'C13': [1, 2, 3, 4],
 'C14': [1, 2, 3, 4],
 'C21': [1, 2, 3, 4],
 'C22': [2],
 'C23': [1, 2, 3, 4],
 'C24': [1, 2, 3, 4],
 'C31': [1, 2, 3, 4],
 'C32': [1, 2, 3, 4],
 'C33': [3],
 'C34': [1, 2, 3, 4],
 'C41': [1, 2, 3, 4],
 'C42': [1, 2, 3, 4],
 'C43': [1, 2, 3, 4],
 'C44': [4]}
[2, 3, 4]

它应该从“C12”中删除1,而不是从“C13”中删除。为什么?我猜和记忆位置有关吧?这真让我抓狂。任何建议都将不胜感激!