fitlog_callback修复

fastNLP/core/callbacks/fitlog_callback.py

@@ -1,8 +1,10 @@
 __all__ = [
     'FitlogCallback'
 ]
-from fastNLP import HasMonitorCallback
-import fitlog
+from .has_monitor_callback import HasMonitorCallback
+from ...envs import _module_available
+if _module_available('fitlog'):
+    import fitlog
 
 
 class FitlogCallback(HasMonitorCallback):
@@ -25,6 +27,8 @@ class FitlogCallback(HasMonitorCallback):
         :param log_exception: 是否记录 ``exception`` 。
         :param log_loss_every: 多少个 ``batch`` 记录一次 loss 到 ``fitlog`` 中。
         """
+        assert _module_available('fitlog'), "fitlog is not installed."
+
         super().__init__(monitor=monitor, larger_better=larger_better)
         self.log_exception = log_exception
         self.log_loss_every = log_loss_every