Make Wrapper with a informative str repr.

qlib/utils/__init__.py

@@ -722,6 +722,10 @@ class Wrapper:
     def register(self, provider):
         self._provider = provider
 
+    def __repr__(self):
+        return ('{name}(provider={provider})'.format(name=self.__class__.__name__,
+                                                     provider=self._provider))
+
     def __getattr__(self, key):
         if self._provider is None:
             raise AttributeError("Please run qlib.init() first using qlib")