add (and test) explicit warning message

IAMconsortium · Jun 16, 2020 · 9b4c904 · 9b4c904
1 parent e74d504
commit 9b4c904
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Showing 2 changed files with 8 additions and 2 deletions.
diff --git a/pyam/core.py b/pyam/core.py
@@ -100,7 +100,10 @@ class IamDataFrame(object):
     """
     def __init__(self, data, **kwargs):
         """Initialize an instance of an IamDataFrame"""
-        if isinstance(data, IamDataFrame) and not kwargs:
+        if isinstance(data, IamDataFrame):
+            if kwargs:
+                msg = 'Invalid arguments `{}` for initializing an IamDataFrame'
+                raise ValueError(msg.format(kwargs))
             for attr, value in data.__dict__.items():
                 setattr(self, attr, value)
         else:

diff --git a/tests/test_core.py b/tests/test_core.py
@@ -62,7 +62,10 @@ def test_init_from_iamdf(test_df_year):
 
 def test_init_from_iamdf_raises(test_df_year):
     # casting an IamDataFrame instance again with extra args fails
-    pytest.raises(ValueError, IamDataFrame, test_df_year, model='foo')
+    args = dict(model='foo')
+    match = f'Invalid arguments `{args}` for initializing an IamDataFrame'
+    with pytest.raises(ValueError, match=match):
+        IamDataFrame(test_df_year, **args)
 
 
 def test_init_df_with_float_cols_raises(test_pd_df):