NF: add reshape_dataobj function

At some point soon, we plan to add a `reshape` method to some arrayproxy
objects.  Make space for that extension to the API, by adding a function
that selects that method when possible, otherwise falling back to the
numpy array API.

Author: matthew-brett

nibabel/arrayproxy.py

@@ -27,6 +27,8 @@
 """
 import warnings
 
+import numpy as np
+
 from .volumeutils import array_from_file, apply_read_scaling
 from .fileslice import fileslice
 from .keywordonly import kw_only_meth
@@ -164,3 +166,10 @@ def is_proxy(obj):
         return obj.is_proxy
     except AttributeError:
         return False
+
+
+def reshape_dataobj(obj, shape):
+    """ Use `obj` reshape method if possible, else numpy reshape function
+    """
+    return (obj.reshape(shape) if hasattr(obj, 'reshape')
+            else np.reshape(obj, shape))

nibabel/tests/test_arrayproxy.py

@@ -17,7 +17,7 @@
 
 import numpy as np
 
-from ..arrayproxy import ArrayProxy, is_proxy
+from ..arrayproxy import ArrayProxy, is_proxy, reshape_dataobj
 from ..nifti1 import Nifti1Header
 
 from numpy.testing import assert_array_equal, assert_array_almost_equal
@@ -158,6 +158,33 @@ class NP(object):
     assert_false(is_proxy(NP()))
 
 
+def test_reshape_dataobj():
+    # Test function that reshapes using method if possible
+    shape = (1, 2, 3, 4)
+    hdr = FunkyHeader(shape)
+    bio = BytesIO()
+    prox = ArrayProxy(bio, hdr)
+    arr = np.arange(np.prod(shape), dtype=prox.dtype).reshape(shape)
+    bio.write(b'\x00' * prox.offset + arr.tostring(order='F'))
+    assert_array_equal(prox, arr)
+    assert_array_equal(reshape_dataobj(prox, (2, 3, 4)),
+                       np.reshape(arr, (2, 3, 4)))
+    assert_equal(prox.shape, shape)
+    assert_equal(arr.shape, shape)
+    assert_array_equal(reshape_dataobj(arr, (2, 3, 4)),
+                       np.reshape(arr, (2, 3, 4)))
+    assert_equal(arr.shape, shape)
+
+    class ArrGiver(object):
+
+        def __array__(self):
+            return arr
+
+    assert_array_equal(reshape_dataobj(ArrGiver(), (2, 3, 4)),
+                       np.reshape(arr, (2, 3, 4)))
+    assert_equal(arr.shape, shape)
+
+
 def test_get_unscaled():
     # Test fetch of raw array
     class FunkyHeader2(FunkyHeader):