In io.ascii, fall back to string if integers are too large

CHANGES.rst

@@ -194,6 +194,10 @@ Bug Fixes
 
 - ``astropy.io.ascii``
 
+  - When reading a table with values that generate an overflow error
+    during type conversion (e.g. overflowing the native C long type), fall
+    through to using string. Previously this generated an exception [#2234].
+
 - ``astropy.io.fits``
 
 - ``astropy.io.misc``

astropy/io/ascii/core.py

@@ -16,10 +16,12 @@
 import itertools
 import functools
 import numpy
+import warnings
 
 from ...extern import six
 from ...extern.six.moves import zip
 from ...extern.six.moves import cStringIO as StringIO
+from ...utils.exceptions import AstropyWarning
 
 from ...table import Table
 from ...utils.data import get_readable_fileobj
@@ -642,6 +644,12 @@ def _convert_vals(self, cols):
                     col.type = converter_type
                 except (TypeError, ValueError):
                     col.converters.pop(0)
+                except OverflowError:
+                    # Overflow during conversion (most likely an int that doesn't fit in native C long).
+                    # Put string at the top of the converters list for the next while iteration.
+                    warnings.warn("OverflowError converting to {0} for column {1}, using string instead."
+                                  .format(converter_type.__name__, col.name), AstropyWarning)
+                    col.converters.insert(0, convert_numpy(numpy.str))
                 except IndexError:
                     raise ValueError('Column %s failed to convert' % col.name)
 

astropy/io/ascii/tests/test_read.py

@@ -11,11 +11,28 @@
 from ... import ascii as asciitable  # TODO: delete this line, use ascii.*
 from ... import ascii
 from ....table import Table
+from distutils import version
 
 from .common import (raises, assert_equal, assert_almost_equal,
                      assert_true, setup_function, teardown_function)
 from ....tests.helper import pytest
 
+_NUMPY_VERSION = version.LooseVersion(np.__version__)
+
+def test_convert_overflow():
+    """
+    Test reading an extremely large integer, which falls through to
+    string due to an overflow error (#2234).
+    """
+    # Before Numpy 1.6 the exception from np.array(['1' * 10000], dtype=np.int)
+    # is exactly the same as np.array(['abc'], dtype=np.int).  In this case
+    # it falls through to float, so we just accept this as a known issue for
+    # numpy < 1.6.
+    expected_kind = ('f',) if _NUMPY_VERSION < version.LooseVersion('1.6') else ('S', 'U')
+    dat = ascii.read(['a', '1' * 10000], format='basic', guess=False)
+    assert dat['a'].dtype.kind in expected_kind
+
+
 def test_guess_with_names_arg():
     """
     Make sure reading a table with guess=True gives the expected result when

docs/known_issues.rst

@@ -184,3 +184,15 @@ One workaround is to install the ``bsddb3`` module.
 .. [#] Continuum `says
        <https://groups.google.com/a/continuum.io/forum/#!topic/anaconda/mCQL6fVx55A>`_
        this will be fixed in their next Python build.
+
+
+Very long integers in ASCII tables silently converted to float for Numpy 1.5
+----------------------------------------------------------------------------
+
+For Numpy 1.5, when reading an ASCII table that has integers which are too
+large to fit into the native C long int type for the machine, then the
+values get converted to float type with no warning.  This is due to the
+behavior of `numpy.array` and cannot easily be worked around.  We recommend
+that users upgrade to a newer version of Numpy.  For Numpy >= 1.6 a warning
+is printed and the values are treated as strings to preserve all information.
+