Make lzma.{encode,decode}_filter_properties private.

These functions were originally added to support LZMA compression in the zipfile
module, and are not of interest for the majority of users.

They can be made public in 3.4 if there is user interest, but in the meanwhile,
I've opted to present a smaller, simpler API for the module's initial release.

Doc/library/lzma.rst

@@ -268,32 +268,6 @@ Miscellaneous
    feature set.
 
 
-.. function:: encode_filter_properties(filter)
-
-   Return a :class:`bytes` object encoding the options (properties) of the
-   filter specified by *filter* (a dictionary).
-
-   *filter* is interpreted as a filter specifier, as described in
-   :ref:`filter-chain-specs`.
-
-   The returned data does not include the filter ID itself, only the options.
-
-   This function is primarily of interest to users implementing custom file
-   formats.
-
-
-.. function:: decode_filter_properties(filter_id, encoded_props)
-
-   Return a dictionary describing a filter with ID *filter_id*, and options
-   (properties) decoded from the :class:`bytes` object *encoded_props*.
-
-   The returned dictionary is a filter specifier, as described in
-   :ref:`filter-chain-specs`.
-
-   This function is primarily of interest to users implementing custom file
-   formats.
-
-
 .. _filter-chain-specs:
 
 Specifying custom filter chains

Lib/lzma.py

@@ -19,12 +19,12 @@ __all__ = [
 
     "LZMACompressor", "LZMADecompressor", "LZMAFile", "LZMAError",
     "open", "compress", "decompress", "is_check_supported",
-    "encode_filter_properties", "decode_filter_properties",
 ]
 
 import builtins
 import io
 from _lzma import *
+from _lzma import _encode_filter_properties, _decode_filter_properties
 
 
 _MODE_CLOSED   = 0

Lib/test/test_lzma.py

@@ -1073,19 +1073,19 @@ class MiscellaneousTestCase(unittest.TestCase):
         # This value should not be a valid check ID.
         self.assertFalse(lzma.is_check_supported(lzma.CHECK_UNKNOWN))
 
-    def test_encode_filter_properties(self):
+    def test__encode_filter_properties(self):
         with self.assertRaises(TypeError):
-            lzma.encode_filter_properties(b"not a dict")
+            lzma._encode_filter_properties(b"not a dict")
         with self.assertRaises(ValueError):
-            lzma.encode_filter_properties({"id": 0x100})
+            lzma._encode_filter_properties({"id": 0x100})
         with self.assertRaises(ValueError):
-            lzma.encode_filter_properties({"id": lzma.FILTER_LZMA2, "junk": 12})
+            lzma._encode_filter_properties({"id": lzma.FILTER_LZMA2, "junk": 12})
         with self.assertRaises(lzma.LZMAError):
-            lzma.encode_filter_properties({"id": lzma.FILTER_DELTA,
+            lzma._encode_filter_properties({"id": lzma.FILTER_DELTA,
                                            "dist": 9001})
 
         # Test with parameters used by zipfile module.
-        props = lzma.encode_filter_properties({
+        props = lzma._encode_filter_properties({
                 "id": lzma.FILTER_LZMA1,
                 "pb": 2,
                 "lp": 0,
@@ -1094,14 +1094,14 @@ class MiscellaneousTestCase(unittest.TestCase):
             })
         self.assertEqual(props, b"]\x00\x00\x80\x00")
 
-    def test_decode_filter_properties(self):
+    def test__decode_filter_properties(self):
         with self.assertRaises(TypeError):
-            lzma.decode_filter_properties(lzma.FILTER_X86, {"should be": bytes})
+            lzma._decode_filter_properties(lzma.FILTER_X86, {"should be": bytes})
         with self.assertRaises(lzma.LZMAError):
-            lzma.decode_filter_properties(lzma.FILTER_DELTA, b"too long")
+            lzma._decode_filter_properties(lzma.FILTER_DELTA, b"too long")
 
         # Test with parameters used by zipfile module.
-        filterspec = lzma.decode_filter_properties(
+        filterspec = lzma._decode_filter_properties(
                 lzma.FILTER_LZMA1, b"]\x00\x00\x80\x00")
         self.assertEqual(filterspec["id"], lzma.FILTER_LZMA1)
         self.assertEqual(filterspec["pb"], 2)
@@ -1110,10 +1110,10 @@ class MiscellaneousTestCase(unittest.TestCase):
         self.assertEqual(filterspec["dict_size"], 8 << 20)
 
     def test_filter_properties_roundtrip(self):
-        spec1 = lzma.decode_filter_properties(
+        spec1 = lzma._decode_filter_properties(
                 lzma.FILTER_LZMA1, b"]\x00\x00\x80\x00")
-        reencoded = lzma.encode_filter_properties(spec1)
-        spec2 = lzma.decode_filter_properties(lzma.FILTER_LZMA1, reencoded)
+        reencoded = lzma._encode_filter_properties(spec1)
+        spec2 = lzma._decode_filter_properties(lzma.FILTER_LZMA1, reencoded)
         self.assertEqual(spec1, spec2)
 
 

Lib/zipfile.py

@@ -495,9 +495,9 @@ class LZMACompressor:
         self._comp = None
 
     def _init(self):
-        props = lzma.encode_filter_properties({'id': lzma.FILTER_LZMA1})
+        props = lzma._encode_filter_properties({'id': lzma.FILTER_LZMA1})
         self._comp = lzma.LZMACompressor(lzma.FORMAT_RAW, filters=[
-                lzma.decode_filter_properties(lzma.FILTER_LZMA1, props)
+                lzma._decode_filter_properties(lzma.FILTER_LZMA1, props)
         ])
         return struct.pack('<BBH', 9, 4, len(props)) + props
 
@@ -529,7 +529,7 @@ class LZMADecompressor:
                 return b''
 
             self._decomp = lzma.LZMADecompressor(lzma.FORMAT_RAW, filters=[
-                    lzma.decode_filter_properties(lzma.FILTER_LZMA1,
+                    lzma._decode_filter_properties(lzma.FILTER_LZMA1,
                             self._unconsumed[4:4 + psize])
             ])
             data = self._unconsumed[4 + psize:]

Modules/_lzmamodule.c

@@ -1097,19 +1097,16 @@ is_check_supported(PyObject *self, PyObject *args)
 }
 
 
-PyDoc_STRVAR(encode_filter_properties_doc,
-"encode_filter_properties(filter) -> bytes\n"
+PyDoc_STRVAR(_encode_filter_properties_doc,
+"_encode_filter_properties(filter) -> bytes\n"
 "\n"
 "Return a bytes object encoding the options (properties) of the filter\n"
 "specified by *filter* (a dict).\n"
 "\n"
-"The result does not include the filter ID itself, only the options.\n"
-"\n"
-"This function is primarily of interest to users implementing custom\n"
-"file formats.\n");
+"The result does not include the filter ID itself, only the options.\n");
 
 static PyObject *
-encode_filter_properties(PyObject *self, PyObject *args)
+_encode_filter_properties(PyObject *self, PyObject *args)
 {
     PyObject *filterspec;
     lzma_filter filter;
@@ -1117,7 +1114,7 @@ encode_filter_properties(PyObject *self, PyObject *args)
     uint32_t encoded_size;
     PyObject *result = NULL;
 
-    if (!PyArg_ParseTuple(args, "O:encode_filter_properties", &filterspec))
+    if (!PyArg_ParseTuple(args, "O:_encode_filter_properties", &filterspec))
         return NULL;
 
     if (parse_filter_spec(&filter, filterspec) == NULL)
@@ -1146,24 +1143,21 @@ error:
 }
 
 
-PyDoc_STRVAR(decode_filter_properties_doc,
-"decode_filter_properties(filter_id, encoded_props) -> dict\n"
+PyDoc_STRVAR(_decode_filter_properties_doc,
+"_decode_filter_properties(filter_id, encoded_props) -> dict\n"
 "\n"
 "Return a dict describing a filter with ID *filter_id*, and options\n"
-"(properties) decoded from the bytes object *encoded_props*.\n"
-"\n"
-"This function is primarily of interest to users implementing custom\n"
-"file formats.\n");
+"(properties) decoded from the bytes object *encoded_props*.\n");
 
 static PyObject *
-decode_filter_properties(PyObject *self, PyObject *args)
+_decode_filter_properties(PyObject *self, PyObject *args)
 {
     Py_buffer encoded_props;
     lzma_filter filter;
     lzma_ret lzret;
     PyObject *result = NULL;
 
-    if (!PyArg_ParseTuple(args, "O&y*:decode_filter_properties",
+    if (!PyArg_ParseTuple(args, "O&y*:_decode_filter_properties",
                           lzma_vli_converter, &filter.id, &encoded_props))
         return NULL;
 
@@ -1187,10 +1181,10 @@ decode_filter_properties(PyObject *self, PyObject *args)
 static PyMethodDef module_methods[] = {
     {"is_check_supported", (PyCFunction)is_check_supported,
      METH_VARARGS, is_check_supported_doc},
-    {"encode_filter_properties", (PyCFunction)encode_filter_properties,
-     METH_VARARGS, encode_filter_properties_doc},
-    {"decode_filter_properties", (PyCFunction)decode_filter_properties,
-     METH_VARARGS, decode_filter_properties_doc},
+    {"_encode_filter_properties", (PyCFunction)_encode_filter_properties,
+     METH_VARARGS, _encode_filter_properties_doc},
+    {"_decode_filter_properties", (PyCFunction)_decode_filter_properties,
+     METH_VARARGS, _decode_filter_properties_doc},
     {NULL}
 };