Merge pull request #4588 from ddasilva/ddasilva/2591

ENH: Better error w/ line num for bad column count in np.loadtxt()

2 files changed, 18 insertions, 2 deletions

diff --git a/numpy/lib/npyio.py b/numpy/lib/npyio.py
index f69ca0c73..98b4b6e35 100644
--- a/numpy/lib/npyio.py
+++ b/numpy/lib/npyio.py
@@ -845,6 +845,11 @@ def loadtxt(fname, dtype=float, comments='#', delimiter=None,
                 continue
             if usecols:
                 vals = [vals[i] for i in usecols]
+            if len(vals) != N:
+                line_num = i + skiprows + 1
+                raise ValueError("Wrong number of columns at line %d"
+                                 % line_num)
+
             # Convert each value according to its column and store
             items = [conv(val) for (conv, val) in zip(converters, vals)]
             # Then pack it according to the dtype's nesting
diff --git a/numpy/lib/tests/test_io.py b/numpy/lib/tests/test_io.py
index 418386e35..d0f81bde3 100644
--- a/numpy/lib/tests/test_io.py
+++ b/numpy/lib/tests/test_io.py
@@ -19,10 +19,13 @@ from numpy.lib._iotools import (ConverterError, ConverterLockError,
                                 ConversionWarning)
 from numpy.compat import asbytes, asbytes_nested, bytes, asstr
 from nose import SkipTest
-from numpy.ma.testutils import (TestCase, assert_equal, assert_array_equal,
-                                assert_raises, run_module_suite)
+from numpy.ma.testutils import (
+    TestCase, assert_equal, assert_array_equal,
+    assert_raises, assert_raises_regex, run_module_suite
+)
 from numpy.testing import assert_warns, assert_, build_err_msg
 
+
 @contextlib.contextmanager
 def tempdir(change_dir=False):
     tmpdir = mkdtemp()
@@ -759,6 +762,14 @@ class TestLoadTxt(TestCase):
         res = np.loadtxt(count())
         assert_array_equal(res, np.arange(10))
 
+    def test_bad_line(self):
+        c = TextIO()
+        c.write('1 2 3\n4 5 6\n2 3')
+        c.seek(0)
+
+        # Check for exception and that exception contains line number
+        assert_raises_regex(ValueError, "3", np.loadtxt, c)
+
 
 class Testfromregex(TestCase):
     # np.fromregex expects files opened in binary mode.