Thanks for the patch. I can see why it's needed.

But, this is not CPython compatible, and we strive to retain compatibility where possible.

Now,file.readinto(buf, size) is also not CPython compatible, and that's really where the trouble begins. Supporting the second argument there means all file-like objects passed intoTarFile must support this 2-argreadinto form.

So I suggest to fix it by changing howskip works, so it doesn't use the 2-arg form, eg:

--- a/python-stdlib/tarfile/tarfile/__init__.py+++ b/python-stdlib/tarfile/tarfile/__init__.py@@ -55,9 +55,12 @@ class FileSection:         if sz:             buf = bytearray(16)             while sz:-                s = min(sz, 16)-                self.f.readinto(buf, s)-                sz -= s+                if sz >= 16:+                    self.f.readinto(buf)+                    sz -= 16+                else:+                    self.f.read(sz)+                    sz = 0   class TarInfo:

For reference, this used to work, but commit2ca1527 optimisedskip to not use too much memory.

[...] Supporting the second argument there means all file-like objects passed intoTarFile must support this 2-argreadinto form.

I thought this was already the case, because as it is, it doesn't work without 2-argumentreadinto at all, even the outer tarfile can't be extracted.

So I suggest to fix it by changing howskip works, so it doesn't use the 2-arg form, eg:

Sure, wilco. I'll also change the title of the PR

I thought this was already the case, because as it is, it doesn't work without 2-argumentreadinto at all, even the outer tarfile can't be extracted.

Yes, you're right, all fileobj's that it uses must support 2-argreadinto. For the most part that's OK, all C-based MicroPython streams will implement that. But Python-based files/stream won't.

For example, if there's a tar file on the host PC and you usempremote mount . and then at the REPL try to usetarfile.TarFile to open the tar file on the mounted host PC, it'll fail with the same problem as this PR is addressing:

  File "tarfile/__init__.py", line 129, in __next__  File "tarfile/__init__.py", line 106, in next  File "tarfile/__init__.py", line 59, in skipTypeError: function takes 2 positional arguments but 3 were given

So, instead of trying to add the 2-arg form to all streams/files, better to fix it once here so that it doesn't use the 2-arg form.

I agree, yes, this sounds like the correct fix. I'll do that the week after; next week I'm on vacation.