added helper function to flatten gf_struct objects for new triqs version

python/triqs_dft_tools/block_structure.py

@@ -1157,5 +1157,45 @@ class BlockStructure(object):
         s += str(self.transformation)
         return s
 
+def gf_struct_flatten(gf_struct):
+    '''
+    flattens gf_struct objecti
+
+    input gf_struct can looks like this:
+
+    [('up', [0, 1, 2]), ('down', [0, 1, 2])]
+
+    and will be returned as
+
+    [('up', 3), ('down', 3)]
+
+    Same for dict but replacing the values. This is for compatibility with the upcoming triqs releases.
+
+    Parameters
+    ----------
+    gf_struct: list of tuple or dict representing the Gf structure
+    __Returns:__
+    gf_struct_flat: flattens the values of the dict or the tuple representing the Gf indices by replacing them with the len of the list of indices
+
+    '''
+
+    if isinstance(gf_struct, list):
+        # create a copy of the original list
+        gf_struct_flat = gf_struct.copy()
+        for idx, block in enumerate(gf_struct_flat):
+            # exchange list of indices with length of list
+            gf_struct_flat[idx] = (block[0], len(block[1]))
+    elif isinstance(gf_struct, dict):
+        # create a copy of the original dict
+        gf_struct_flat = dict(gf_struct)
+        for key, value in gf_struct_flat.items():
+            # exchange list of indices with length of list
+            gf_struct_flat[key] = len(value)
+    else:
+        raise Exception('gf_struct input needs to be list or dict')
+
+
+    return gf_struct_flat
+
 from h5.formats import register_class
 register_class(BlockStructure)