diff --git a/field.py b/field.py
index 4b48c9a..b13e2da 100644
--- a/field.py
+++ b/field.py
@@ -135,7 +135,7 @@ class Field3d:
 
     def save(self,file,name='Field3d',truncate=False):
         import h5py
-        is_open = isinstance(file,h5py.File)
+        is_open = isinstance(file,(h5py.File,h5py.Group))
         flag = 'w' if truncate else 'a'
         f = file if is_open else h5py.File(file,flag)
         g = f.create_group(name)
diff --git a/helper.py b/helper.py
index 2c21422..3ed71b5 100644
--- a/helper.py
+++ b/helper.py
@@ -64,4 +64,21 @@ def load_matv73(f,var,squeeze=True,cast_string=True,cast_integer=False):
                         squeeze=squeeze,
                         cast_string=cast_string,
                         cast_integer=cast_integer)
-        return d
\ No newline at end of file
+        return d
+
+def h5write(file,arr,name='data',truncate=True):
+    import h5py
+    is_open = isinstance(file,(h5py.File,h5py.Group))
+    flag = 'w' if truncate else 'a'
+    f = file if is_open else h5py.File(file,flag)
+    f.create_dataset(name,data=arr)
+    if not is_open: f.close()
+    return
+
+def h5read(file,name='data'):
+    import h5py
+    is_open = isinstance(file,(h5py.File,h5py.Group))
+    f = file if is_open else h5py.File(file,'r')
+    data = f[name][:]
+    if not is_open: f.close()
+    return data
\ No newline at end of file