improve informative error around columns

mrocklin · Jul 6, 2015 · 8ad9a4c · 8ad9a4c
1 parent 0ad5a04
commit 8ad9a4c
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Showing 2 changed files with 11 additions and 1 deletion.
diff --git a/dask/dataframe/io.py b/dask/dataframe/io.py
@@ -495,7 +495,8 @@ def from_dask_array(x, columns=None):
         if columns is None:
             raise ValueError("Must provide columns for DataFrame")
         if len(columns) != x.shape[1]:
-            raise ValueError("Columns must be the same length as array width")
+            raise ValueError("Columns must be the same length as array width\n"
+                    "  columns: %s\n  width: %d" % (str(columns), x.shape[1]))
         if len(x.chunks[1]) > 1:
             x = x.rechunk({1: x.shape[1]})
         dsk = dict(((name, i), (pd.DataFrame, chunk[0], ind, columns))

diff --git a/dask/dataframe/tests/test_io.py b/dask/dataframe/tests/test_io.py
@@ -361,3 +361,12 @@ def test_from_dask_array_raises():
 
     x = da.ones((10, 3), chunks=(3, 3))
     pytest.raises(ValueError, lambda: from_dask_array(x))  # no columns
+
+    # Not enough columns
+    pytest.raises(ValueError, lambda: from_dask_array(x, columns=['a']))
+
+    try:
+        from_dask_array(x, columns=['hello'])
+    except Exception as e:
+        assert 'hello' in str(e)
+        assert '3' in str(e)