If run this code, it will raise an exception: 

    import pickle
    import lzma
    import pandas as pd
    with lzma.open("test.xz", "wb") as file:
        pickle.dump(pd.DataFrame(range(1_000_000)), file, protocol=5)

The exception:

    Traceback (most recent call last):
      File "E:\testlen.py", line 7, in <module>
        pickle.dump(pd.DataFrame(range(1_000_000)), file, protocol=5)
      File "D:\Python39\lib\lzma.py", line 234, in write
        self._pos += len(data)
    TypeError: object of type 'pickle.PickleBuffer' has no len()
    
The exception is raised in lzma.LZMAFile.write() method:
https://github.com/python/cpython/blob/v3.10.0b2/Lib/lzma.py#L238
        
PickleBuffer doesn't have .__len__ method, is it intended?

Oh, LZMAFile.write() should not use len() directly on input data because it does not always work correctly with memoryview and other objects supporting the buffer protocol. It should use memoryview(data).nbytes or data = memoryview(data).cast('B') if other byte-oriented operations (indexing, slicing) are used. See for example Lib/gzip.py, Lib/_pyio.py, Lib/_compression.py, Lib/ssl.py, Lib/socketserver.py, Lib/wave.py.

Ok, I'm working on a PR.

I am checking all the .py files in `Lib` folder.
hmac.py has two len() bugs:
https://github.com/python/cpython/blob/v3.10.0b3/Lib/hmac.py#L212
https://github.com/python/cpython/blob/v3.10.0b3/Lib/hmac.py#L214

I think PR 26764 is prepared, it fixes the len() bugs in bz2.py/lzma.py files.

New changeset bc6c12c72a9536acc96e7b9355fd69d1083a43c1 by Ma Lin in branch 'main':
bpo-44439: BZ2File.write() / LZMAFile.write() handle buffer protocol correctly (GH-26764)
https://github.com/python/cpython/commit/bc6c12c72a9536acc96e7b9355fd69d1083a43c1

New changeset 8bc26d8c9d092840054f57f9b4620de0d40d8423 by Ma Lin in branch '3.9':
bpo-44439: BZ2File.write()/LZMAFile.write() handle length correctly (GH-26846)
https://github.com/python/cpython/commit/8bc26d8c9d092840054f57f9b4620de0d40d8423

Thank you for your contribution Ma Lin.

New changeset 01858fbe31e8e0185edfbd3f10172f7c61391c9d by Miss Islington (bot) in branch '3.10':
bpo-44439: BZ2File.write() / LZMAFile.write() handle buffer protocol correctly (GH-26764) (GH-26845)
https://github.com/python/cpython/commit/01858fbe31e8e0185edfbd3f10172f7c61391c9d

Serhiy Storchaka:

Sorry, I found `zipfile` module also has this bug, fixed in PR29468.

This bug was reported & fixed by GitHub user `marcoffee` firstly, so I list him as a co-author, his work:
https://github.com/animalize/pyzstd/issues/4

The second commit fixes an omission of issue41735, a very simple fix, I fix it in PR29468 by the way.

New changeset 36dd7396fcd26d8bf9919d536d05d7000becbe5b by Ma Lin in branch 'main':
bpo-44439: _ZipWriteFile.write() handle buffer protocol correctly (GH-29468)
https://github.com/python/cpython/commit/36dd7396fcd26d8bf9919d536d05d7000becbe5b

New changeset 21c5b3f73fb11fb0d3239971f72e8f0574a07245 by Miss Islington (bot) in branch '3.10':
bpo-44439: _ZipWriteFile.write() handle buffer protocol correctly (GH-29468)
https://github.com/python/cpython/commit/21c5b3f73fb11fb0d3239971f72e8f0574a07245

New changeset 0663ca17f5535178c083c6734fa52e40bd2db2de by Miss Islington (bot) in branch '3.9':
bpo-44439: _ZipWriteFile.write() handle buffer protocol correctly (GH-29468)
https://github.com/python/cpython/commit/0663ca17f5535178c083c6734fa52e40bd2db2de

Can this be closed now or is there anything else to do?

`_Stream.write` method in tarfile.py also has this code:
https://github.com/python/cpython/blob/v3.11.0a6/Lib/tarfile.py#L434

But this bug will not be triggered. When calling this method, always pass bytes data.

`_ConnectionBase.send_bytes` method in multiprocessing\connection.py can be micro-optimized:
https://github.com/python/cpython/blob/v3.11.0a6/Lib/multiprocessing/connection.py#L193
This can be done in another issue.

So I think this issue can be closed.