Handle nested dictionaries in config parameter storage

invisible_cities/cities/components.py

@@ -211,10 +211,37 @@ def index_tables(file_out):
                 table.colinstances[colname].create_index()
 
 
+def dict_to_string(arg : dict,
+                   parent_key : str= ""):
+    '''
+    A function that recusively flattens nested dictionaries and converts the values to strings.
+
+    Each nested key is combined with its parent keys and associated with its respective value 
+    as a string.
+
+    Parameters
+    ----------
+    arg        : the dictionary to flatten which can contain nested dictionaries
+    parent_key : the string containing the prefix to use for keys in the flattened dictionary (default "").
+
+    Returns
+    -------
+    flat_dict : flattened dictionary containing no nested dictionaries and where all values are strings
+    '''
+    flat_dict = {}
+    for k, v in arg.items():
+        new_key = f"{parent_key}.{k}" if parent_key else k
+        if isinstance(v, dict):
+            flat_dict.update(dict_to_string(v, new_key))
+        else:
+            flat_dict[new_key] = str(v)
+    return flat_dict
+
+
 def write_city_configuration( filename : str
                             , city_name: str
                             , args     : dict):
-    args = {k: str(v) for k,v in args.items()}
+    args = dict_to_string(args)
 
     with tb.open_file(filename, "a") as file:
         df = (pd.Series(args)

invisible_cities/cities/components_test.py

@@ -560,17 +560,26 @@ def test_write_city_configuration(config_tmpdir):
         d = "two strings".split(),
         e = [1,2,3],
         f = np.linspace(0, 1, 5),
+        g = {'a' : 2, 'b' : 3, 'c' : {'alpha' : 5, 'beta' : 10}}
     )
     write_city_configuration(filename, city_name, args)
     with tb.open_file(filename, "r") as file:
         assert "config"  in file.root
         assert city_name in file.root.config
 
     df = pd.read_hdf(filename, "/config/" + city_name).set_index("variable")
-    for var, value in args.items():
+
+    # ignoring the nested dictionary
+    for var, value in list(args.items())[:-1]:
         assert var in df.index
         assert str(value) == df.value.loc[var]
 
+    # considering just the nested dictionary
+    assert 'g.a'        in df.index  and str(args['g']['a'])           == df.value.loc['g.a']
+    assert 'g.b'        in df.index  and str(args['g']['b'])           == df.value.loc['g.b']
+    assert 'g.c.alpha'  in df.index  and str(args['g']['c']['alpha'])  == df.value.loc['g.c.alpha']
+    assert 'g.c.beta'   in df.index  and str(args['g']['c']['beta'])   == df.value.loc['g.c.beta']
+
 
 def test_copy_cities_configuration(config_tmpdir):
     filename1  = os.path.join(config_tmpdir, "test_copy_cities_configuration_1.h5")