Try this

tzis/__init__.py

-from . import tzis
+from .tzis import Tzis

tzis/tzis.py

@@ -9,7 +9,7 @@ import shutil
 import math
 from tqdm import tqdm
 
-class tzis:
+class Tzis:
     def __init__(self,                 
                  mf_dset=None,
                  varname=None,