BUG: Prevent infinite recursion when printing self-containing arrays

Fixes #8960

2 files changed, 64 insertions, 2 deletions

diff --git a/numpy/core/arrayprint.py b/numpy/core/arrayprint.py
index 4e62a42fc..dba9dffb3 100644
--- a/numpy/core/arrayprint.py
+++ b/numpy/core/arrayprint.py
@@ -16,7 +16,18 @@ __docformat__ = 'restructuredtext'
 # and by Travis Oliphant  2005-8-22 for numpy
 
 import sys
-from functools import reduce
+import functools
+if sys.version_info[0] >= 3:
+    try:
+        from _thread import get_ident
+    except ImportError:
+        from _dummy_thread import get_ident
+else:
+    try:
+        from thread import get_ident
+    except ImportError:
+        from dummy_thread import get_ident
+
 from . import numerictypes as _nt
 from .umath import maximum, minimum, absolute, not_equal, isnan, isinf
 from .multiarray import (array, format_longfloat, datetime_as_string,
@@ -342,6 +353,39 @@ def _array2string(a, max_line_width, precision, suppress_small, separator=' ',
                        _summaryEdgeItems, summary_insert)[:-1]
     return lst
 
+
+def _recursive_guard(fillvalue='...'):
+    """
+    Like the python 3.2 reprlib.recursive_repr, but forwards *args and **kwargs
+
+    Decorates a function such that if it calls itself with the same first
+    argument, it returns `fillvalue` instead of recursing.
+
+    Largely copied from reprlib.recursive_repr
+    """
+
+    def decorating_function(f):
+        repr_running = set()
+
+        @functools.wraps(f)
+        def wrapper(self, *args, **kwargs):
+            key = id(self), get_ident()
+            if key in repr_running:
+                return fillvalue
+            repr_running.add(key)
+            try:
+                return f(self, *args, **kwargs)
+            finally:
+                repr_running.discard(key)
+
+        return wrapper
+
+    return decorating_function
+
+
+# gracefully handle recursive calls - this comes up when object arrays contain
+# themselves
+@_recursive_guard()
 def array2string(a, max_line_width=None, precision=None,
                  suppress_small=None, separator=' ', prefix="",
                  style=repr, formatter=None):
@@ -460,7 +504,7 @@ def array2string(a, max_line_width=None, precision=None,
             lst = format_function(arr[0])
         else:
             lst = style(x)
-    elif reduce(product, a.shape) == 0:
+    elif functools.reduce(product, a.shape) == 0:
         # treat as a null array if any of shape elements == 0
         lst = "[]"
     else:
diff --git a/numpy/core/tests/test_arrayprint.py b/numpy/core/tests/test_arrayprint.py
index 62effc425..b228527da 100644
--- a/numpy/core/tests/test_arrayprint.py
+++ b/numpy/core/tests/test_arrayprint.py
@@ -34,6 +34,24 @@ class TestArrayRepr(object):
             "    dtype=[('a', '<i4')])"
         )
 
+    def test_self_containing(self):
+        arr0d = np.array(None)
+        arr0d[()] = arr0d
+        assert_equal(repr(arr0d),
+            'array(array(..., dtype=object), dtype=object)')
+
+        arr1d = np.array([None, None])
+        arr1d[1] = arr1d
+        assert_equal(repr(arr1d),
+            'array([None, array(..., dtype=object)], dtype=object)')
+
+        first = np.array(None)
+        second = np.array(None)
+        first[()] = second
+        second[()] = first
+        assert_equal(repr(first),
+            'array(array(array(..., dtype=object), dtype=object), dtype=object)')
+
 
 class TestComplexArray(TestCase):
     def test_str(self):