Merge pull request #17878 from MaiaKaplan/arange_keyword

BUG: np.arange: Allow `stop` not `start` as sole kwargs. 

2 files changed, 29 insertions, 1 deletions

diff --git a/numpy/core/src/multiarray/multiarraymodule.c b/numpy/core/src/multiarray/multiarraymodule.c
index af5949e73..79956863a 100644
--- a/numpy/core/src/multiarray/multiarraymodule.c
+++ b/numpy/core/src/multiarray/multiarraymodule.c
@@ -2878,7 +2878,7 @@ array_arange(PyObject *NPY_UNUSED(ignored), PyObject *args, PyObject *kws) {
     static char *kwd[] = {"start", "stop", "step", "dtype", "like", NULL};
     PyArray_Descr *typecode = NULL;
 
-    if (!PyArg_ParseTupleAndKeywords(args, kws, "O|OOO&$O:arange", kwd,
+    if (!PyArg_ParseTupleAndKeywords(args, kws, "|OOOO&$O:arange", kwd,
                 &o_start,
                 &o_stop,
                 &o_step,
@@ -2888,6 +2888,18 @@ array_arange(PyObject *NPY_UNUSED(ignored), PyObject *args, PyObject *kws) {
         return NULL;
     }
 
+    if (o_stop == NULL) {
+        if (args == NULL || PyTuple_GET_SIZE(args) == 0){
+            PyErr_SetString(PyExc_TypeError,
+                "arange() requires stop to be specified.");
+            return NULL;
+        }
+    }
+    else if (o_start == NULL) {
+        o_start = o_stop;
+        o_stop = NULL;
+    }
+
     array_function_result = array_implement_c_array_function_creation(
             "arange", args, kws);
     if (array_function_result != Py_NotImplemented) {
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index bd8c51ab7..2df92ee65 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -8473,6 +8473,22 @@ class TestArange:
         assert_raises(ZeroDivisionError, np.arange, 0, 0, 0)
         assert_raises(ZeroDivisionError, np.arange, 0.0, 0.0, 0.0)
 
+    def test_require_range(self):
+        assert_raises(TypeError, np.arange)
+        assert_raises(TypeError, np.arange, step=3)
+        assert_raises(TypeError, np.arange, dtype='int64')
+        assert_raises(TypeError, np.arange, start=4)
+
+    def test_start_stop_kwarg(self):
+        keyword_stop = np.arange(stop=3)
+        keyword_zerotostop = np.arange(start=0, stop=3)
+        keyword_start_stop = np.arange(start=3, stop=9)
+
+        assert len(keyword_stop) == 3
+        assert len(keyword_zerotostop) == 3
+        assert len(keyword_start_stop) == 6
+        assert_array_equal(keyword_stop, keyword_zerotostop)
+
 
 class TestArrayFinalize:
     """ Tests __array_finalize__ """