1 files changed, 113 insertions, 1 deletions
diff --git a/Lib/test/test_slice.py b/Lib/test/test_slice.py
index 2df9271da7..9203d5eb19 100644
--- a/Lib/test/test_slice.py
+++ b/Lib/test/test_slice.py
@@ -4,8 +4,70 @@ import unittest
 from test import support
 from pickle import loads, dumps
 
+import itertools
+import operator
 import sys
 
+
+def evaluate_slice_index(arg):
+    """
+    Helper function to convert a slice argument to an integer, and raise
+    TypeError with a suitable message on failure.
+
+    """
+    if hasattr(arg, '__index__'):
+        return operator.index(arg)
+    else:
+        raise TypeError(
+            "slice indices must be integers or "
+            "None or have an __index__ method")
+
+def slice_indices(slice, length):
+    """
+    Reference implementation for the slice.indices method.
+
+    """
+    # Compute step and length as integers.
+    length = operator.index(length)
+    step = 1 if slice.step is None else evaluate_slice_index(slice.step)
+
+    # Raise ValueError for negative length or zero step.
+    if length < 0:
+        raise ValueError("length should not be negative")
+    if step == 0:
+        raise ValueError("slice step cannot be zero")
+
+    # Find lower and upper bounds for start and stop.
+    lower = -1 if step < 0 else 0
+    upper = length - 1 if step < 0 else length
+
+    # Compute start.
+    if slice.start is None:
+        start = upper if step < 0 else lower
+    else:
+        start = evaluate_slice_index(slice.start)
+        start = max(start + length, lower) if start < 0 else min(start, upper)
+
+    # Compute stop.
+    if slice.stop is None:
+        stop = lower if step < 0 else upper
+    else:
+        stop = evaluate_slice_index(slice.stop)
+        stop = max(stop + length, lower) if stop < 0 else min(stop, upper)
+
+    return start, stop, step
+
+
+# Class providing an __index__ method.  Used for testing slice.indices.
+
+class MyIndexable(object):
+    def __init__(self, value):
+        self.value = value
+
+    def __index__(self):
+        return self.value
+
+
 class SliceTest(unittest.TestCase):
 
     def test_constructor(self):
@@ -75,6 +137,22 @@ class SliceTest(unittest.TestCase):
         s = slice(obj)
         self.assertTrue(s.stop is obj)
 
+    def check_indices(self, slice, length):
+        try:
+            actual = slice.indices(length)
+        except ValueError:
+            actual = "valueerror"
+        try:
+            expected = slice_indices(slice, length)
+        except ValueError:
+            expected = "valueerror"
+        self.assertEqual(actual, expected)
+
+        if length >= 0 and slice.step != 0:
+            actual = range(*slice.indices(length))
+            expected = range(length)[slice]
+            self.assertEqual(actual, expected)
+
     def test_indices(self):
         self.assertEqual(slice(None           ).indices(10), (0, 10,  1))
         self.assertEqual(slice(None,  None,  2).indices(10), (0, 10,  2))
@@ -108,7 +186,41 @@ class SliceTest(unittest.TestCase):
 
         self.assertEqual(list(range(10))[::sys.maxsize - 1], [0])
 
-        self.assertRaises(OverflowError, slice(None).indices, 1<<100)
+        # Check a variety of start, stop, step and length values, including
+        # values exceeding sys.maxsize (see issue #14794).
+        vals = [None, -2**100, -2**30, -53, -7, -1, 0, 1, 7, 53, 2**30, 2**100]
+        lengths = [0, 1, 7, 53, 2**30, 2**100]
+        for slice_args in itertools.product(vals, repeat=3):
+            s = slice(*slice_args)
+            for length in lengths:
+                self.check_indices(s, length)
+        self.check_indices(slice(0, 10, 1), -3)
+
+        # Negative length should raise ValueError
+        with self.assertRaises(ValueError):
+            slice(None).indices(-1)
+
+        # Zero step should raise ValueError
+        with self.assertRaises(ValueError):
+            slice(0, 10, 0).indices(5)
+
+        # Using a start, stop or step or length that can't be interpreted as an
+        # integer should give a TypeError ...
+        with self.assertRaises(TypeError):
+            slice(0.0, 10, 1).indices(5)
+        with self.assertRaises(TypeError):
+            slice(0, 10.0, 1).indices(5)
+        with self.assertRaises(TypeError):
+            slice(0, 10, 1.0).indices(5)
+        with self.assertRaises(TypeError):
+            slice(0, 10, 1).indices(5.0)
+
+        # ... but it should be fine to use a custom class that provides index.
+        self.assertEqual(slice(0, 10, 1).indices(5), (0, 5, 1))
+        self.assertEqual(slice(MyIndexable(0), 10, 1).indices(5), (0, 5, 1))
+        self.assertEqual(slice(0, MyIndexable(10), 1).indices(5), (0, 5, 1))
+        self.assertEqual(slice(0, 10, MyIndexable(1)).indices(5), (0, 5, 1))
+        self.assertEqual(slice(0, 10, 1).indices(MyIndexable(5)), (0, 5, 1))
 
     def test_setslice_without_getslice(self):
         tmp = []