字符串中有列表如何把列表提取出来？

file = ['[1,2,3],[4,5,6],[7,8,9]']
data = file[0]

number = []
alist = []
count = 0 
i = 0  


char = ['[', ',', ']']

while i < len(data):
    if data[i] in char:
        i += 1
        
    elif count < 3:
        alist.append(int(data[i]))
        count += 1
        i += 1 
    
    if count == 3:
        number.append(alist)
        alist = []
        count = 0 

print(number)

输出：number = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]