Wrap _PyBytes_Resize for improved usability

The `_PyBytes_Resize` function is helpful for resizing a `bytes` object
after it is allocated. When the underlying `bytes` object only has one
reference to it, the function can potentially use realloc to shrink or
grow the allocation in-place.

While the function signature of `_PyBytes_Resize` makes sense, it is a
little unwieldly when used directly in Cython. To smooth this out a
bit, use a macro to wrap calls to `_PyBytes_Resize`. This allows us to
work with `PyObject*`s, which Cython handles well, instead of
`PyObject**`s, which Cython handles awkwardly.

The end result is a function from Cython's perspective, which is easy to
use, and one under-the-hood that simply massages our input arguments
into something `_PyBytes_Resize` expects.

Author: jakirkham

numcodecs/blosc.pyx

@@ -13,16 +13,21 @@ from cpython.buffer cimport PyBuffer_IsContiguous
 from cpython.bytes cimport (
     PyBytes_AS_STRING,
     PyBytes_FromStringAndSize,
-    _PyBytes_Resize,
 )
 from cpython.memoryview cimport PyMemoryView_GET_BUFFER
-from cpython.object cimport PyObject
 
 
 from .compat import ensure_contiguous_ndarray
 from .abc import Codec
 
 
+cdef extern from *:
+    """
+    #define PyBytes_RESIZE(b, n) _PyBytes_Resize(&b, n)
+    """
+    int PyBytes_RESIZE(object b, Py_ssize_t n) except -1
+
+
 cdef extern from "blosc.h":
     cdef enum:
         BLOSC_MAX_OVERHEAD,
@@ -276,7 +281,6 @@ def compress(source, char* cname, int clevel, int shuffle=SHUFFLE,
         size_t nbytes, itemsize
         int cbytes
         bytes dest
-        PyObject* dest_objptr
         char* dest_ptr
 
     # check valid cname early
@@ -356,9 +360,7 @@ def compress(source, char* cname, int clevel, int shuffle=SHUFFLE,
         raise RuntimeError('error during blosc compression: %d' % cbytes)
 
     # resize after compression
-    dest_objptr = <PyObject*>dest
-    _PyBytes_Resize(&dest_objptr, cbytes)
-    dest = <bytes>dest_objptr
+    PyBytes_RESIZE(dest, cbytes)
 
     return dest
 

numcodecs/lz4.pyx

@@ -11,16 +11,21 @@ from cpython.buffer cimport PyBuffer_IsContiguous
 from cpython.bytes cimport (
     PyBytes_AS_STRING,
     PyBytes_FromStringAndSize,
-    _PyBytes_Resize,
 )
 from cpython.memoryview cimport PyMemoryView_GET_BUFFER
-from cpython.object cimport PyObject
 
 from ._utils cimport store_le32, load_le32
 from .compat import ensure_contiguous_ndarray
 from .abc import Codec
 
 
+cdef extern from *:
+    """
+    #define PyBytes_RESIZE(b, n) _PyBytes_Resize(&b, n)
+    """
+    int PyBytes_RESIZE(object b, Py_ssize_t n) except -1
+
+
 cdef extern from "lz4.h":
 
     const char* LZ4_versionString() nogil
@@ -74,7 +79,6 @@ def compress(source, int acceleration=DEFAULT_ACCELERATION):
         const Py_buffer* source_pb
         const char* source_ptr
         bytes dest
-        PyObject* dest_objptr
         char* dest_ptr
         char* dest_start
         int source_size, dest_size, compressed_size
@@ -115,9 +119,7 @@ def compress(source, int acceleration=DEFAULT_ACCELERATION):
 
     # resize after compression
     compressed_size += sizeof(uint32_t)
-    dest_objptr = <PyObject*>dest
-    _PyBytes_Resize(&dest_objptr, compressed_size)
-    dest = <bytes>dest_objptr
+    PyBytes_RESIZE(dest, compressed_size)
 
     return dest
 

numcodecs/zstd.pyx

@@ -9,15 +9,20 @@ from cpython.buffer cimport PyBuffer_IsContiguous
 from cpython.bytes cimport (
     PyBytes_AS_STRING,
     PyBytes_FromStringAndSize,
-    _PyBytes_Resize,
 )
 from cpython.memoryview cimport PyMemoryView_GET_BUFFER
-from cpython.object cimport PyObject
 
 from .compat import ensure_contiguous_ndarray
 from .abc import Codec
 
 
+cdef extern from *:
+    """
+    #define PyBytes_RESIZE(b, n) _PyBytes_Resize(&b, n)
+    """
+    int PyBytes_RESIZE(object b, Py_ssize_t n) except -1
+
+
 cdef extern from "zstd.h":
 
     unsigned ZSTD_versionNumber() nogil
@@ -100,7 +105,6 @@ def compress(source, int level=DEFAULT_CLEVEL, bint checksum=False):
         const char* source_ptr
         size_t source_size, dest_size, compressed_size
         bytes dest
-        PyObject* dest_objptr
         char* dest_ptr
 
     # check level
@@ -151,9 +155,7 @@ def compress(source, int level=DEFAULT_CLEVEL, bint checksum=False):
         raise RuntimeError('Zstd compression error: %s' % error)
 
     # resize after compression
-    dest_objptr = <PyObject*>dest
-    _PyBytes_Resize(&dest_objptr, compressed_size)
-    dest = <bytes>dest_objptr
+    PyBytes_RESIZE(dest, compressed_size)
 
     return dest