BUG: Fix segfault in `random.permutation(x)` when x is a string. (#14241)

* fixing segfault error in np.random.permutation(x) where x is str

* removed whitespace

* changing error type to ValueError

* changing error type to ValueError

* changing error type to ValueError

* tests

* changed error to IndexError for backward compatibility with numpy 1.16

* fixes numpy.randomstate.permutation segfault too

* Rolled back to ValueError for Generator.permutation() for all 0-dimensional

* fixes refuige erro and rolls backs to AxisError

4 files changed, 40 insertions, 2 deletions

diff --git a/numpy/random/generator.pyx b/numpy/random/generator.pyx
index c7432d8c1..26fd95129 100644
--- a/numpy/random/generator.pyx
+++ b/numpy/random/generator.pyx
@@ -3919,9 +3919,8 @@ cdef class Generator:
         permutation(x)
 
         Randomly permute a sequence, or return a permuted range.
-
         If `x` is a multi-dimensional array, it is only shuffled along its
-        first index.
+        first index. 
 
         Parameters
         ----------
@@ -3950,13 +3949,20 @@ cdef class Generator:
                [0, 1, 2],
                [3, 4, 5]])
 
+        >>> rng.permutation("abc")
+        Traceback (most recent call last):
+            ...
+        numpy.AxisError: x must be an integer or at least 1-dimensional
         """
+
         if isinstance(x, (int, np.integer)):
             arr = np.arange(x)
             self.shuffle(arr)
             return arr
 
         arr = np.asarray(x)
+        if arr.ndim < 1:
+            raise np.AxisError("x must be an integer or at least 1-dimensional")
 
         # shuffle has fast-path for 1-d
         if arr.ndim == 1:
diff --git a/numpy/random/mtrand.pyx b/numpy/random/mtrand.pyx
index 46b6b3388..eb263cd2d 100644
--- a/numpy/random/mtrand.pyx
+++ b/numpy/random/mtrand.pyx
@@ -4134,6 +4134,7 @@ cdef class RandomState:
         out : ndarray
             Permuted sequence or array range.
 
+
         Examples
         --------
         >>> np.random.permutation(10)
@@ -4149,12 +4150,15 @@ cdef class RandomState:
                [3, 4, 5]])
 
         """
+
         if isinstance(x, (int, np.integer)):
             arr = np.arange(x)
             self.shuffle(arr)
             return arr
 
         arr = np.asarray(x)
+        if arr.ndim < 1:
+            raise IndexError("x must be an integer or at least 1-dimensional")
 
         # shuffle has fast-path for 1-d
         if arr.ndim == 1:
diff --git a/numpy/random/tests/test_generator_mt19937.py b/numpy/random/tests/test_generator_mt19937.py
index a962fe84e..853d86fba 100644
--- a/numpy/random/tests/test_generator_mt19937.py
+++ b/numpy/random/tests/test_generator_mt19937.py
@@ -757,6 +757,19 @@ class TestRandomDist(object):
         arr_2d = np.atleast_2d([1, 2, 3, 4, 5, 6, 7, 8, 9, 0]).T
         actual = random.permutation(arr_2d)
         assert_array_equal(actual, np.atleast_2d(desired).T)
+        
+        bad_x_str = "abcd"
+        assert_raises(np.AxisError, random.permutation, bad_x_str)
+
+        bad_x_float = 1.2
+        assert_raises(np.AxisError, random.permutation, bad_x_float)
+
+        random = Generator(MT19937(self.seed))
+        integer_val = 10
+        desired = [3, 0, 8, 7, 9, 4, 2, 5, 1, 6]
+
+        actual = random.permutation(integer_val)
+        assert_array_equal(actual, desired)
 
     def test_beta(self):
         random = Generator(MT19937(self.seed))
diff --git a/numpy/random/tests/test_randomstate.py b/numpy/random/tests/test_randomstate.py
index 3b5a279a3..a0edc5c23 100644
--- a/numpy/random/tests/test_randomstate.py
+++ b/numpy/random/tests/test_randomstate.py
@@ -686,6 +686,21 @@ class TestRandomDist(object):
         actual = random.permutation(arr_2d)
         assert_array_equal(actual, np.atleast_2d(desired).T)
 
+        random.seed(self.seed)
+        bad_x_str = "abcd"
+        assert_raises(IndexError, random.permutation, bad_x_str)
+
+        random.seed(self.seed)
+        bad_x_float = 1.2
+        assert_raises(IndexError, random.permutation, bad_x_float)
+
+        integer_val = 10
+        desired = [9, 0, 8, 5, 1, 3, 4, 7, 6, 2]
+
+        random.seed(self.seed)
+        actual = random.permutation(integer_val)
+        assert_array_equal(actual, desired)
+
     def test_beta(self):
         random.seed(self.seed)
         actual = random.beta(.1, .9, size=(3, 2))