BUG: Move ctypes ImportError catching to appropriate place (#8898)

This fixes a regression in 3c1a13dea6a7e189675977ad65ea230ce4816061, restoring the
behaviour intended by eee00f8f7e15592a048c8b841aef9ea81faa0fda.

This also extends the support on ctype-less systems for `arr.ctypes.shape` and `arr.ctypes.strides`.

The dummy_ctype object is a naive fake used when ctypes is not importable. It does not intend to fake any ctypes behavior, but provides a duck-typed interface so that method calls do not fail.

The get_shape and get_strides refactors take advantage of other instance methods and reduce code duplication.

2 files changed, 52 insertions, 17 deletions

diff --git a/numpy/core/_internal.py b/numpy/core/_internal.py
index 01741cd1a..d8d9168ac 100644
--- a/numpy/core/_internal.py
+++ b/numpy/core/_internal.py
@@ -11,7 +11,10 @@ import sys
 
 from numpy.compat import basestring
 from .multiarray import dtype, array, ndarray
-import ctypes
+try:
+    import ctypes
+except ImportError:
+    ctypes = None
 from .numerictypes import object_
 
 if (sys.byteorder == 'little'):
@@ -194,19 +197,33 @@ def _commastring(astr):
 
     return result
 
+class dummy_ctype(object):
+    def __init__(self, cls):
+        self._cls = cls
+    def __mul__(self, other):
+        return self
+    def __call__(self, *other):
+        return self._cls(other)
+    def __eq__(self, other):
+        return self._cls == other._cls
+
 def _getintp_ctype():
     val = _getintp_ctype.cache
     if val is not None:
         return val
-    char = dtype('p').char
-    if (char == 'i'):
-        val = ctypes.c_int
-    elif char == 'l':
-        val = ctypes.c_long
-    elif char == 'q':
-        val = ctypes.c_longlong
+    if ctypes is None:
+        import numpy as np
+        val = dummy_ctype(np.intp)
     else:
-        val = ctypes.c_long
+        char = dtype('p').char
+        if (char == 'i'):
+            val = ctypes.c_int
+        elif char == 'l':
+            val = ctypes.c_long
+        elif char == 'q':
+            val = ctypes.c_longlong
+        else:
+            val = ctypes.c_long
     _getintp_ctype.cache = val
     return val
 _getintp_ctype.cache = None
@@ -222,9 +239,9 @@ class _missing_ctypes(object):
 
 class _ctypes(object):
     def __init__(self, array, ptr=None):
-        try:
+        if ctypes:
             self._ctypes = ctypes
-        except ImportError:
+        else:
             self._ctypes = _missing_ctypes()
         self._arr = array
         self._data = ptr
@@ -250,14 +267,10 @@ class _ctypes(object):
         return self._data
 
     def get_shape(self):
-        if self._zerod:
-            return None
-        return (_getintp_ctype()*self._arr.ndim)(*self._arr.shape)
+        return self.shape_as(_getintp_ctype())
 
     def get_strides(self):
-        if self._zerod:
-            return None
-        return (_getintp_ctype()*self._arr.ndim)(*self._arr.strides)
+        return self.strides_as(_getintp_ctype())
 
     def get_as_parameter(self):
         return self._ctypes.c_void_p(self._data)
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index 4dc82eb1d..8ab8c0ca7 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -6742,6 +6742,28 @@ class TestUnicodeArrayNonzero(TestCase):
         a[0] = ' \0 \0'
         self.assertTrue(a)
 
+
+class TestCTypes(TestCase):
+
+    def test_ctypes_is_available(self):
+        test_arr = np.array([[1, 2, 3], [4, 5, 6]])
+
+        self.assertEqual(ctypes, test_arr.ctypes._ctypes)
+        assert_equal(tuple(test_arr.ctypes.shape), (2, 3))
+
+    def test_ctypes_is_not_available(self):
+        from numpy.core import _internal
+        _internal.ctypes = None
+        try:
+            test_arr = np.array([[1, 2, 3], [4, 5, 6]])
+
+            self.assertIsInstance(
+                test_arr.ctypes._ctypes, _internal._missing_ctypes)
+            assert_equal(tuple(test_arr.ctypes.shape), (2, 3))
+        finally:
+            _internal.ctypes = ctypes
+
+
 def test_orderconverter_with_nonASCII_unicode_ordering():
     # gh-7475
     a = np.arange(5)