Merge pull request #315 from liaozd/python-opt

nums为一个list，不需要判断为空就可以做join

Author: wangzheng0822

python/06_linkedlist/singly_linked_list.py

@@ -106,10 +106,7 @@ def __repr__(self) -> str:
         while current:
             nums.append(current.data)
             current = current._next
-        if len(nums) > 0:
-            return "->".join(str(num) for num in nums)
-        else:
-            return ""
+        return "->".join(str(num) for num in nums)
 
     # 重写__iter__方法，方便for关键字调用打印值
     def __iter__(self):