log_str += ', '.join(log_items)

log_str += ', '.join(log_items)
这行是 Python 里很常见的 字符串拼接 + join 语法，拆开看其实很简单。
用 ", " 作为分隔符，把 list 里的字符串拼成一个长字符串

log_items = ["loss: 1.0", "lr: 0.001", "time: 0.5"]

result = ', '.join(log_items)
#loss: 1.0, lr: 0.001, time: 0.5

log_items = []
        for name, val in log_dict.items():
            # TODO: resolve this hack
            # these items have been in log_str
            if name in [
                    'mode', 'Epoch', 'iter', 'lr', 'time', 'data_time',
                    'memory', 'epoch'
            ]:
                continue
            if isinstance(val, float):
                val = f'{val:.4f}'
            log_items.append(f'{name}: {val}')
        log_str += ', '.join(log_items)

2026-05-19 20:45:13,430 - mmdet - INFO - Epoch [1][150/27015] lr: 1.064e-04, eta: 67 days, 19:02:59, time: 1.130, data_time: 0.017, memory: 8456, loss_cls_0: 1.6042, loss_reg_0: 2.1852, loss_cls_1: 1.5532, loss_reg_1: 2.2024, loss_cls_2: 1.5287, loss_reg_2: 2.1910, loss_cls_3: 1.5370, loss_reg_3: 2.1937, loss_cls_4: 1.5375, loss_reg_4: 2.2282, loss_cls_5: 1.5239, loss_reg_5: 2.2710, loss_depth: 1.3339, loss: 23.8899, grad_norm: 104.1702