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_pyio.TextIOBase.readline is missing a size arg #151596
Description
Bug report
Bug description:
IOBase:
Line 513 in a064b32
TextIOBase:
Line 1931 in a064b32
This pattern seems to be missing only for readline AFAICT.
for truncate (which is also "unsupported" for TextIOBase) it's preserved:
IOBase:
Line 370 in a064b32
TextIOBase:
Line 1927 in a064b32
(the same for write and others).
My proposed fix should be adding a size argument to readline with a default value of -1
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Linked PRs
- gh-151596: Added missing argument 'size' with default value of -1 to TextIOBase.readline #151679
- gh-151596: Add size to _pyio.TextIOBase.readline #151680
- [3.15] gh-151596: Add missing argument 'size' to pure-Python implementation of
TextIOBase.readline(GH-151679) #151870 - [3.14] gh-151596: Add missing argument 'size' to pure-Python implementation of
TextIOBase.readline(GH-151679) #151871 - [3.13] gh-151596: Add missing argument 'size' to pure-Python implementation of
TextIOBase.readline(GH-151679) #151872
Activity
picnixz commentedon Jun 17, 2026
cc @cmaloney
cmaloney commentedon Jun 17, 2026
truncateis a bit different as "The current stream position isn’t changed" (https://docs.python.org/3/library/io.html#io.IOBase.truncate).In the C implementation
_io.TextIOWrapper,_io.BufferedIO, and_io.BytesIOdo take an optionalsizeargument today so this works as specified today._pyiotakes one in_pyio.TextIOWrapper.readline._pyioisn't used in production anywhere as far as I'm aware and it's only the_pyio.TextIOBase.readlinewhich is an abstract method missing thesize=. I'm open to a tiny patch without NEWS addingsizeto_pyio.TextIOBase.readlineit but I am doubtful that is worth the time / effort to write, review, and ship as_pyiois a CPython internal module.[-]`_pyio.TextIOBase.read` is missing a `size` arg[/-][+]`_pyio.TextIOBase.readline` is missing a `size` arg[/+]ZeroIntensity commentedon Jun 19, 2026
I don't understand this.
_pyiois a fallback when the C version ofioisn't available, isn't it? Why is it considered internal?cmaloney commentedon Jun 19, 2026
As currently coded it's not used as a fallback and requires
_io/ the C version to build/run.ZeroIntensity commentedon Jun 20, 2026
I suspect that other implementations might be using it anyway.
_iocan be written in an implementation's native language to get the primitive aspects, and then use_pyiofrom there to get the rest of the module.That said, this is a bit of a gray area. Do you know of any precedent to point to here?
cmaloney commentedon Jun 20, 2026
I looked at some of the other Python implementations (ex. PyPy) that have been brought up and all I have investigated either use
_ioor have a fully independent implementation of theioAPI. Have had some in person conversations around what makes sense for_pyiolong term. All that said a NEWS file is not going to cause harm here; I thought it would lead to more review round trips and wasn't really valuable hence trying to just leave out for the one line patch.ZeroIntensity commentedon Jun 20, 2026
Yeah, no worries, I'm just being pedantic :)
gh-151596: Add missing argument 'size' to pure-Python implementation …
ZeroIntensity commentedon Jun 22, 2026
Any strong opinions on whether we backport this to 3.13 and 3.14?
vstinner commentedon Jun 22, 2026
Oh. I read again the issue: the
iomodule already has thesizeparameter inreadline(). This change is only for the Python implementation which is not used by default.So I changed my mind and I'm fine with backporting the change to stable versions.
[3.15] gh-151596: Add missing argument 'size' to pure-Python implemen…
[3.14] gh-151596: Add missing argument 'size' to pure-Python implemen…
[3.13] gh-151596: Add missing argument 'size' to pure-Python implemen…
pythongh-151596: Add missing argument 'size' to pure-Python implement…