Enable renaming of an empty IamDataFrame (#668)

.github/workflows/build-docs.yml

@@ -25,10 +25,10 @@ jobs:
     name: ${{ matrix.os }} py${{ matrix.python-version }}
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: ${{ matrix.python-version }}
 

.github/workflows/nightly.yml

@@ -27,10 +27,10 @@ jobs:
     name: ${{ matrix.os }} py${{ matrix.python-version }}
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: ${{ matrix.python-version }}
 

.github/workflows/pytest-dependency.yml

@@ -15,10 +15,10 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - name: Set up Python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: '3.7'
 

.github/workflows/pytest.yml

@@ -30,10 +30,10 @@ jobs:
     name: ${{ matrix.os }} py${{ matrix.python-version }}
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: ${{ matrix.python-version }}
 

pyam/core.py

@@ -1107,6 +1107,10 @@ def rename(
             raise ValueError(f"Conflicting rename args for columns {duplicate}")
         mapping.update(kwargs)
 
+        # return without any changes if self is empty
+        if self.empty:
+            return self if inplace else self.copy()
+
         # determine columns that are not in the meta index
         meta_idx = self.meta.index.names
         data_cols = set(self.dimensions) - set(meta_idx)

tests/test_feature_rename.py

@@ -6,6 +6,7 @@
 from numpy import testing as npt
 
 from pyam import IamDataFrame, META_IDX, IAMC_IDX, compare
+from pyam.testing import assert_iamframe_equal
 
 from .conftest import META_COLS
 
@@ -191,6 +192,12 @@ def test_rename_conflict(test_df):
     pytest.raises(ValueError, test_df.rename, mapping, **mapping)
 
 
+def test_rename_empty(test_df_year):
+    """Check that renaming an empty IamDataFrame does not raise an error"""
+    empty_df = test_df_year.filter(model="foo")
+    assert_iamframe_equal(empty_df, empty_df.rename(model={"model_a": "model_b"}))
+
+
 def test_rename_index_data_fail(test_df):
     mapping = {
         "scenario": {"scen_a": "scen_c"},