numpy · ghost · Mar 5, 2017 · Mar 7, 2017 · Mar 8, 2017 · Mar 26, 2017
diff --git a/doc/release/1.13.0-notes.rst b/doc/release/1.13.0-notes.rst
@@ -229,6 +229,12 @@ array, in the same way that ``sort`` already did. Additionally, the
 Note that this argument is not added at the end, so breaks any code that
 passed ``fill_value`` as a positional argument.
 
+``randint`` and ``choice`` now work on empty distributions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Even when no elements needed to be drawn, ``np.random.randint`` and
+``np.random.choice`` raised an error when the arguments described an empty
+distribution. This has been fixed so that e.g.
+``np.random.choice([],0) == np.array([],dtype=float64)``.
 Bundled version of LAPACK is now 3.2.2
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 NumPy comes bundled with a minimal implementation of lapack for systems without

diff --git a/numpy/random/mtrand/mtrand.pyx b/numpy/random/mtrand/mtrand.pyx
@@ -22,8 +22,8 @@
 # SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 include "Python.pxi"
-include "randint_helpers.pxi"
 include "numpy.pxd"
+include "randint_helpers.pxi"
 include "cpython/pycapsule.pxd"
 
 from libc cimport string
@@ -973,8 +973,8 @@ cdef class RandomState:
             raise ValueError("low is out of bounds for %s" % (key,))
         if high > highbnd:
             raise ValueError("high is out of bounds for %s" % (key,))
-        if low >= high:
-            raise ValueError("low >= high")
+        if low >= high and np.prod(size) != 0:
+            raise ValueError("Range cannot be empty (low >= high) unless no samples are taken")
 
         with self.lock:
             ret = randfunc(low, high - 1, size, self.state_address)
@@ -1100,14 +1100,14 @@ cdef class RandomState:
                pop_size = operator.index(a.item())
             except TypeError:
                 raise ValueError("a must be 1-dimensional or an integer")
-            if pop_size <= 0:
-                raise ValueError("a must be greater than 0")
+            if pop_size <= 0 and np.prod(size) != 0:
+                raise ValueError("a must be greater than 0 unless no samples are taken")
         elif a.ndim != 1:
             raise ValueError("a must be 1-dimensional")
         else:
             pop_size = a.shape[0]
-            if pop_size is 0:
-                raise ValueError("a must be non-empty")
+            if pop_size is 0 and np.prod(size) != 0:
+                raise ValueError("a cannot be empty unless no samples are taken")
 
         if p is not None:
             d = len(p)

diff --git a/numpy/random/mtrand/randint_helpers.pxi.in b/numpy/random/mtrand/randint_helpers.pxi.in
@@ -23,7 +23,7 @@ def get_dispatch(dtypes):
 
 {{for npy_dt, npy_udt, np_dt in get_dispatch(dtypes)}}
 
-def _rand_{{npy_dt}}(low, high, size, rngstate):
+def _rand_{{npy_dt}}(npy_{{npy_dt}} low, npy_{{npy_dt}} high, size, rngstate):
     """
     _rand_{{npy_dt}}(low, high, size, rngstate)
 
@@ -60,8 +60,8 @@ def _rand_{{npy_dt}}(low, high, size, rngstate):
     cdef npy_intp cnt
     cdef rk_state *state = <rk_state *>PyCapsule_GetPointer(rngstate, NULL)
 
-    rng = <npy_{{npy_udt}}>(high - low)
-    off = <npy_{{npy_udt}}>(<npy_{{npy_dt}}>low)
+    off = <npy_{{npy_udt}}>(low)
+    rng = <npy_{{npy_udt}}>(high) - <npy_{{npy_udt}}>(low)
 
     if size is None:
         rk_random_{{npy_udt}}(off, rng, 1, &buf, state)

diff --git a/numpy/random/tests/test_random.py b/numpy/random/tests/test_random.py
@@ -389,6 +389,14 @@ def test_choice_return_shape(self):
         assert_equal(np.random.choice(6, s, replace=False, p=p).shape, s)
         assert_equal(np.random.choice(np.arange(6), s, replace=True).shape, s)
 
+        # Check zero-size
+        assert_equal(np.random.randint(0,0,(3,0,4)).shape, (3,0,4))
+        assert_equal(np.random.randint(0,-10,0).shape, (0,))
+        assert_equal(np.random.choice(0,0).shape, (0,))
+        assert_equal(np.random.choice([],(0,)).shape, (0,))
+        assert_equal(np.random.choice(['a', 'b'], size=(3, 0, 4)).shape, (3, 0, 4))
+        assert_raises(ValueError, np.random.choice, [], 10)
+
     def test_bytes(self):
         np.random.seed(self.seed)
         actual = np.random.bytes(10)