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ENH: raise useful error message on invalid concat arguments #3559

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Merged
1 commit merged into from
May 10, 2013
Merged

ENH: raise useful error message on invalid concat arguments #3559

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5 changes: 5 additions & 0 deletions pandas/tools/merge.py
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Original file line number Diff line number Diff line change
Expand Up @@ -888,6 +888,11 @@ class _Concatenator(object):
def __init__(self, objs, axis=0, join='outer', join_axes=None,
keys=None, levels=None, names=None,
ignore_index=False, verify_integrity=False):
if not isinstance(objs, (tuple, list, dict)):
raise AssertionError('first argument must be a list of pandas '
'objects, you passed an object of type '
'"{0}"'.format(type(objs).__name__))

if join == 'outer':
self.intersect = False
elif join == 'inner':
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8 changes: 7 additions & 1 deletion pandas/tools/tests/test_merge.py
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Expand Up @@ -13,7 +13,8 @@
from pandas.tseries.index import DatetimeIndex
from pandas.tools.merge import merge, concat, ordered_merge, MergeError
from pandas.util.testing import (assert_frame_equal, assert_series_equal,
assert_almost_equal, rands)
assert_almost_equal, rands,
makeCustomDataframe as mkdf)
import pandas.algos as algos
import pandas.util.testing as tm

Expand Down Expand Up @@ -1689,6 +1690,11 @@ def test_concat_series_axis1_same_names_ignore_index(self):
result = concat([s1, s2], axis=1, ignore_index=True)
self.assertTrue(np.array_equal(result.columns, [0, 1]))

def test_concat_invalid_first_argument(self):
df1 = mkdf(10, 2)
df2 = mkdf(10, 2)
self.assertRaises(AssertionError, concat, df1, df2)

class TestOrderedMerge(unittest.TestCase):

def setUp(self):
Expand Down