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gh-135648: Document that shutil.copyfileobj doesn't flush #135737

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gh-135648: Document that shutil.copyfileobj doesn't flush #135737

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e3766fd
Add note about flush/close on copyfileobj.
freakboy3742 Jun 20, 2025
6f0d22d
Update emscripten build script to follow documented advice.
freakboy3742 Jun 20, 2025
2ced62b
Remove NEWS entry.
freakboy3742 Jun 21, 2025
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7 changes: 7 additions & 0 deletions Doc/library/shutil.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,13 @@ Directory and files operations
0, only the contents from the current file position to the end of the file will
be copied.

:func:`copyfileobj` will *not* guarantee that the destination stream has
been flushed on completion of the copy. If you want to read from the
destination at the completion of the copy operation (for example, reading
the contents of a temporary file that has been copied from a HTTP stream),
you must ensure that you have called :func:`~io.IOBase.flush` or
:func:`~io.IOBase.close` on the file-like object before attempting to read
the destination file.

.. function:: copyfile(src, dst, *, follow_symlinks=True)

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Documentation/2025-06-20-10-27-11.gh-issue-135648.xCC_zC.rst
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@@ -0,0 +1,2 @@
The documentation for :func:`shutil.copyfileobj` now warns the user of the
need to close or flush the destination stream on completion.
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The Documentation blurb section is usually used for meta changes, e.g. tags or theme, and not entries about changes in the docs?

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I don't think that a NEWS entry is needed.

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Removed.

3 changes: 2 additions & 1 deletion Tools/wasm/emscripten/__main__.py
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Expand Up @@ -167,11 +167,12 @@ def make_build_python(context, working_dir):
@subdir(HOST_BUILD_DIR, clean_ok=True)
def make_emscripten_libffi(context, working_dir):
shutil.rmtree(working_dir / "libffi-3.4.6", ignore_errors=True)
with tempfile.NamedTemporaryFile(suffix=".tar.gz") as tmp_file:
with tempfile.NamedTemporaryFile(suffix=".tar.gz", delete_on_close=False) as tmp_file:
with urlopen(
"https://github.com/libffi/libffi/releases/download/v3.4.6/libffi-3.4.6.tar.gz"
) as response:
shutil.copyfileobj(response, tmp_file)
tmp_file.close()
shutil.unpack_archive(tmp_file.name, working_dir)
call(
[EMSCRIPTEN_DIR / "make_libffi.sh"],
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