gh-139821: Make tarfile.open correctly forward keyword arguments for zstd in stream mode.

Doc/library/tarfile.rst

@@ -137,6 +137,9 @@ Some facts and figures:
    a Zstandard dictionary used to improve compression of smaller amounts of
    data.
 
+   For modes ``'r:zst'`` and ``'r|zst'``, :func:`tarfile.open` accepts the keyword
+   arguments *options* and *zstd_dict* as well.
+
    For special purposes, there is a second format for *mode*:
    ``'filemode|[compression]'``.  :func:`tarfile.open` will return a :class:`TarFile`
    object that processes its data as a stream of blocks.  No random seeking will

Lib/tarfile.py

@@ -338,7 +338,7 @@ class _Stream:
     """
 
     def __init__(self, name, mode, comptype, fileobj, bufsize,
-                 compresslevel, preset):
+                 compresslevel, preset, level, options, zstd_dict):
         """Construct a _Stream object.
         """
         self._extfileobj = True
@@ -405,10 +405,10 @@ def __init__(self, name, mode, comptype, fileobj, bufsize,
                     raise CompressionError("compression.zstd module is not available") from None
                 if mode == "r":
                     self.dbuf = b""
-                    self.cmp = zstd.ZstdDecompressor()
+                    self.cmp = zstd.ZstdDecompressor(zstd_dict, options)
                     self.exception = zstd.ZstdError
                 else:
-                    self.cmp = zstd.ZstdCompressor()
+                    self.cmp = zstd.ZstdCompressor(level, options, zstd_dict)
             elif comptype != "tar":
                 raise CompressionError("unknown compression type %r" % comptype)
 
@@ -1929,10 +1929,20 @@ def not_compressed(comptype):
             if "preset" in kwargs and comptype not in ("xz",):
                 raise ValueError("preset is only valid for w|xz mode")
 
+            if comptype not in ("zst",):
+                for arg in ("level", "options", "zstd_dict"):
+                    if arg in kwargs:
+                        raise ValueError(
+                            f"{arg} is only valid for zstd compression"
+                        )
+
             compresslevel = kwargs.pop("compresslevel", 6)
             preset = kwargs.pop("preset", None)
+            level = kwargs.pop("level", None)
+            options = kwargs.pop("options", None)
+            zstd_dict = kwargs.pop("zstd_dict", None)
             stream = _Stream(name, filemode, comptype, fileobj, bufsize,
-                             compresslevel, preset)
+                             compresslevel, preset, level, options, zstd_dict)
             try:
                 t = cls(name, filemode, stream, **kwargs)
             except:

Misc/NEWS.d/next/Library/2025-10-09-05-42-07.gh-issue-139821.cHM3qC.rst

@@ -0,0 +1 @@
+Make ``tarfile.open`` correctly forward keyword arguments for zstd in stream mode.