ARROW-2252: [Python] Create buffer from address, size and base

python/pyarrow/__init__.py

@@ -72,8 +72,8 @@
 from pyarrow.lib import TimestampType
 
 # Buffers, allocation
-from pyarrow.lib import (Buffer, ResizableBuffer, compress, decompress,
-                         allocate_buffer, frombuffer)
+from pyarrow.lib import (Buffer, ForeignBuffer, ResizableBuffer, compress,
+                         decompress, allocate_buffer, frombuffer)
 
 from pyarrow.lib import (MemoryPool, total_allocated_bytes,
                          set_memory_pool, default_memory_pool,

python/pyarrow/io.pxi

@@ -720,6 +720,18 @@ cdef class Buffer:
         return self.size
 
 
+cdef class ForeignBuffer(Buffer):
+
+    def __init__(self, addr, size, base):
+        cdef:
+            intptr_t c_addr = addr
+            int64_t c_size = size
+        self.base = base
+        cdef shared_ptr[CBuffer] buffer = make_shared[CBuffer](
+            <uint8_t*>c_addr, c_size)
+        self.init(<shared_ptr[CBuffer]> buffer)
+
+
 cdef class ResizableBuffer(Buffer):
 
     cdef void init_rz(self, const shared_ptr[CResizableBuffer]& buffer):

python/pyarrow/lib.pxd

@@ -324,6 +324,11 @@ cdef class Buffer:
     cdef int _check_nullptr(self) except -1
 
 
+cdef class ForeignBuffer(Buffer):
+    cdef:
+        object base
+
+
 cdef class ResizableBuffer(Buffer):
 
     cdef void init_rz(self, const shared_ptr[CResizableBuffer]& buffer)

python/pyarrow/tests/test_io.py

@@ -24,6 +24,7 @@
 import weakref
 
 import numpy as np
+import numpy.testing as npt
 
 import pandas as pd
 
@@ -253,6 +254,14 @@ def test_buffer_equals():
     assert buf2.equals(buf5)
 
 
+def test_foreign_buffer():
+    n = np.array([1, 2])
+    addr = n.__array_interface__["data"][0]
+    size = n.nbytes
+    fb = pa.ForeignBuffer(addr, size, n)
+    npt.assert_array_equal(np.asarray(fb), n.view(dtype=np.int8))
+
+
 def test_allocate_buffer():
     buf = pa.allocate_buffer(100)
     assert buf.size == 100