尝试在其他线程中使用变量时出现UnboundLocalError

Question

我是Python的新手，我需要在一个线程中创建一个矩阵，然后在第二个线程中将主对角线计算为一行和一列中的元素之和

matrix.py

class MyThread(Thread):

    def __init__(self, number, logger):
        Thread.__init__(self)
        self.number = number
        self.logger = logger

    def run(self) :
        if self.number == 0:
            logger.debug('Calling martix()')
            mat = matrix()
        else:
            logger.debug('Calling recalculate()')
            recalculate(mat)

def matrix():
    delimetr = "|"
    print('Enter the size of matrix \n')
    n = int(input())
    print('start at:', ctime())
    mat = [[randint(0,100) for j in range(n)] for i in range(n)]
    print('Before')  
    for i in mat:
        print(delimetr,*i,delimetr)
    return mat

def get_logger():
     logger = logging.getLogger("threading_matrix")
     logger.setLevel(logging.DEBUG)
     fh = logging.FileHandler("threading_matix.log")
     fmt = '%(asctime)s - %(threadName)s - %(levelname)s - %(message)s'
     formatter = logging.Formatter(fmt)
     fh.setFormatter(formatter)
     logger.addHandler(fh)
     return logger

def recalculate(mat):
    delimetr = "|"
    m=0
    score = 0;
    n = len(mat)
    for v in mat:
        score = 0;
        for i in range(n):
            score = mat[m][i] + score
        for b in range(n):
            if b == m : continue
            else:
                score = mat[b][m] + score
        mat[m][m] = score
        m+=1

    print('After')    
    for i in mat:
        print(delimetr,*i,delimetr)
    print('end at:',ctime())

if __name__ == '__main__':
 logger = get_logger()
 for i in range(2):
     name = "Thread #%s" % (i+1)
     thread = MyThread(i, logger)
     thread.setName(name)
     thread.start()
     thread.join()

运行此命令时出现异常

in run recalculate(mat) UnboundLocalError: local variable 'mat' referenced before assignment

我试图将mat设置为全局变量，但这无济于事。