BF: make Bomber raise AttributeError instance

Bomber instance was causing problems for Python 3 inspect module because
it was raising an error for hasattr checks.  Make BomberError that is
instance of AttributeError to allow inspect to - er - inspect.

Author: matthew-brett

nibabel/data.py

@@ -18,7 +18,16 @@
                         'path to the package correctly?')
 
 
-class DataError(OSError):
+class DataError(Exception):
+    pass
+
+
+class BomberError(DataError, AttributeError):
+    """ Error when trying to access Bomber instance
+
+    Should be instance of AttributeError to allow Python 3 inspect to do various
+    ``hasattr`` checks without raising an error
+    """
     pass
 
 
@@ -302,7 +311,7 @@ def __init__(self, name, msg):
 
     def __getattr__(self, attr_name):
         ''' Raise informative error accessing not-found attributes '''
-        raise DataError(
+        raise BomberError(
             'Trying to access attribute "%s" '
             'of non-existent data "%s"\n\n%s\n' %
             (attr_name, self.name, self.msg))

nibabel/tests/test_data.py

@@ -19,8 +19,7 @@
 
 from nose import with_setup
 
-from nose.tools import assert_equal, \
-    assert_raises, raises
+from nose.tools import (assert_equal, assert_raises, raises, assert_false)
 
 from .test_environment import (setup_environment,
                                teardown_environment,
@@ -241,6 +240,11 @@ def test_bomber():
     res = b.any_attribute
 
 
+def test_bomber_inspect():
+    b = Bomber('bomber example', 'a message')
+    assert_false(hasattr(b, 'any_attribute'))
+
+
 @with_environment
 def test_datasource_or_bomber():
     pkg_def = dict(