gh-51067: Add _REPACK_CHUNK_SIZE constant

Single source of truth for the 1 MiB default used by both
ZipFile.repack() and _ZipRepacker.

Author: gpshead

Lib/test/test_zipfile/test_core.py

@@ -1828,7 +1828,8 @@ def test_repack_propagation(self):
             with mock.patch.object(zipfile._ZipRepacker, 'repack') as m_rp, \
                  mock.patch.object(zipfile, '_ZipRepacker', wraps=zipfile._ZipRepacker) as m_zr:
                 zh.repack()
-        m_zr.assert_called_once_with(strict_descriptor=True, chunk_size=2**20)
+        m_zr.assert_called_once_with(strict_descriptor=True,
+                                     chunk_size=zipfile._REPACK_CHUNK_SIZE)
         m_rp.assert_called_once_with(zh, None)
 
         with zipfile.ZipFile(TESTFN, 'a', self.compression) as zh:

Lib/zipfile/__init__.py

@@ -1394,9 +1394,13 @@ def close(self):
             self._zipfile._writing = False
 
 
+_REPACK_CHUNK_SIZE = 2**20
+
+
 class _ZipRepacker:
     """Class for ZipFile repacking."""
-    def __init__(self, *, strict_descriptor=True, chunk_size=2**20, debug=0):
+    def __init__(self, *, strict_descriptor=True,
+                 chunk_size=_REPACK_CHUNK_SIZE, debug=0):
         self.debug = debug  # Level of printing: 0 through 3
         self.chunk_size = chunk_size
         self.strict_descriptor = strict_descriptor
@@ -2388,7 +2392,8 @@ def remove(self, zinfo_or_arcname):
 
         return zinfo
 
-    def repack(self, removed=None, *, strict_descriptor=True, chunk_size=2**20):
+    def repack(self, removed=None, *, strict_descriptor=True,
+               chunk_size=_REPACK_CHUNK_SIZE):
         """Repack a zip file, removing non-referenced file entries.
 
         The archive must be opened with mode 'a', as mode 'w'/'x' do not