Name generated signature parameters the way CPython names them by leehanjeong · Pull Request #8725 · RustPython/RustPython · GitHub

Related Malformed builtin __text_signature__ makes inspect.signature(len/sorted/open) raise ValueError #8383
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Summary

A generated __text_signature__ reports the Rust parameter name, so help(), inspect.signature() and tab completion show whatever name reads well in Rust. Of the 1,591 signatures RustPython and CPython both define, parameter names now match CPython for 1,311, up from 1,171. Nothing that matched before stops matching, and every generated signature still parses.

What changed

The generator drops a leading _ and r# from a parameter name. _ marks an argument Rust doesn't use, and r# escapes a keyword but its # starts a comment in Python, so (r#type, /) fails to parse. This alone fixes _sre.template, select.epoll.__exit__ and bytearray.__reduce_ex__, and lets sys._clear_type_descriptors take the name CPython gives it.
Parameters CPython names differently are renamed, one commit per area: os.read's n to length, sys.excepthook's exc_tb to traceback, unicodedata.category's character to chr, list.pop's i to index, and so on.

Left for #8383

231 of the 1,591 still differ.

The parameter is a FromArgs struct or FuncArgs the generator cannot see into. This covers most of the 182 that disagree on how many parameters there are, and some that only look like a name difference: gc.collect reports (args, /) where CPython reports generation, and os.chmod reports (path, dir_fd, mode, follow_symlinks, /) although os.chmod(p, 0o644) binds mode second and accepts follow_symlinks by keyword. When FromArgs starts reporting its fields, it has to keep a leading _: compile's _feature_version is one, and CPython reports it with the underscore.
A PosArgs parameter is reported as a single positional one, so frozenset.difference is ($self, others, /) where CPython has ($self, /, *others). 10 signatures.
os.statvfs and os.fstatvfs are one Rust function registered twice, so they cannot report CPython's separate path and fd.

Notes

29 parameters CPython reports as object or unused keep their RustPython names. CPython fills these in from the METH_* flags when a function has no signature of its own: slice.indices is ($self, object, /) while its own docstring calls the argument len, and RustPython already reports length. Where the name comes from an Argument Clinic signature, as in list.insert and set.add, the parameter is renamed.
set.__contains__ and frozenset.__contains__ report key where CPython's Clinic signature has object. RustPython exposes them through the __contains__ slot wrapper, while CPython defines them as methods, so test_pydoc's *_coexist_o tests stay marked as expected failures.
set.symmetric_difference accepts any number of arguments, so s.symmetric_difference({2}, {3}) returns a set where CPython raises TypeError. This is a behaviour bug rather than a signature one, left for a separate fix.
.cspell.json learns ustr, CPython's name for array.fromunicode's parameter.
The util.rs change only affects how func_sig spells a name, not how it classifies arguments, in case that bears on the convention mentioned on Stop generating a __text_signature__ that inspect cannot parse #8681.

Assisted-by: Claude Code:claude-opus-5

Summary by CodeRabbit

Refactor
- Clarified parameter names across built-in types and standard-library APIs, including formatting, collections, filesystem, process, signal, compression, and Unicode functionality.
- Improved generated function signatures by normalizing identifier names.
- Updated several Python-facing keyword argument names for consistency; runtime behavior remains unchanged.
Chores
- Updated spelling configuration to recognize an additional valid term.

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⛔ Files ignored due to path filters (1)

Lib/test/test_pydoc/test_pydoc.py is excluded by !Lib/**

📒 Files selected for processing (5)

crates/stdlib/src/array.rs
crates/vm/src/builtins/list.rs
crates/vm/src/builtins/set.rs
crates/vm/src/stdlib/_weakref.rs
crates/vm/src/stdlib/sys.rs

🚧 Files skipped from review as they are similar to previous changes (2)

crates/vm/src/stdlib/_weakref.rs
crates/stdlib/src/array.rs

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📝 Walkthrough

Walkthrough

The PR normalizes generated Rust identifiers and renames parameters across standard-library and VM implementations. Runtime logic remains unchanged. The cspell configuration now accepts ustr.

Changes

Parameter Naming and Identifier Normalization

Layer / File(s)	Summary
Generated identifier normalization .cspell.json, crates/derive-impl/src/util.rs	func_sig now removes raw-identifier syntax and one leading underscore from generated parameter names. ustr is added to the cspell word list.
Standard-library parameter renames crates/stdlib/src/{array,binascii,cmath,math,pystruct,unicodedata,zlib}.rs	Parameters are renamed to descriptive identifiers. Existing validation, conversions, error handling, and operations remain unchanged.
Builtin parameter renames crates/vm/src/builtins/*.rs, crates/vm/src/exception_group.rs	Formatting, collection, object, set, and exception-group parameters are renamed. Recursive calls and method bodies use the renamed variables without logic changes.
VM standard-library parameter renames crates/vm/src/stdlib/{_codecs,_collections,_operator,_signal,_sre,_weakref,itertools,os,posix,sys}.rs	Parameters are renamed across VM standard-library functions. Existing validation, state updates, system calls, and return behavior remain unchanged.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix

Suggested reviewers: youknowone

Merge Risk: ⚪ Minimal · up to c9ffb

This PR aligns generated parameter names with CPython without changing runtime behavior, and is ready to merge.

🚥 Pre-merge checks | ✅ 5 ✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: updating generated signature parameter names to match CPython conventions.
Docstring Coverage	✅ Passed	Docstring coverage is 94.67% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 169 functions across 31 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

[x] lib: cpython/Lib/pydoc.py
[x] lib: cpython/Lib/pydoc_data
[ ] test: cpython/Lib/test/test_pydoc (TODO: 26)

dependencies:

pydoc

dependent tests: (5 tests)

pydoc: test_enum test_pydoc
- pdb: test_pdb
- xmlrpc.server: test_docxmlrpc test_xmlrpc

Legend:

[+] path exists in CPython
[x] up-to-date, [ ] outdated

A leading underscore marks an argument Rust sees as unused and `r#` escapes a Rust keyword. Neither describes the parameter a Python caller passes, and `r#` is not valid Python, so `inspect.signature()` rejects any signature carrying one. Reporting the bare name fixes _sre.template, select.epoll.__exit__ and bytearray.__reduce_ex__ without touching them, and lets a method name a parameter after a Rust keyword. A parameter CPython itself names with a leading underscore, such as compile's `_feature_version`, reaches Python through a FromArgs field, which this never sees. Assisted-by: Claude Code:claude-opus-5

A generated __text_signature__ reports the Rust parameter name, so a name chosen for Rust reaches anyone reading help() or inspect. Rename the ones CPython describes differently: list.pop's `i` becomes `index`, list.count's `needle` becomes `value`, __format__'s `spec` becomes `format_spec`, bytes.strip's `chars` becomes `bytes`, and object.__reduce_ex__'s `proto` becomes `protocol`. Left alone are the parameters CPython reports as `object` or `unused`. Those are synthesised from the METH_* flags rather than named: CPython reports slice.indices as ($self, object, /) while its own docstring calls the argument len. Assisted-by: Claude Code:claude-opus-5

os.read's `n` becomes `length`, os.lseek's `how` becomes `whence`, os.kill's `sig` becomes `signal`, os.stat's `file` becomes `path`, and os.putenv's `key` becomes `name`, among others. os.chmod is left alone. It reports (path, dir_fd, mode, follow_symlinks) while the call binds mode second and takes follow_symlinks by keyword, so the order and the kind are wrong rather than the names, which a rename cannot fix. os.fstatvfs is left alone too: it shares one Rust function with statvfs, which CPython names `path`, so the two aliases cannot report different names. Assisted-by: Claude Code:claude-opus-5

sys.excepthook's (exc_type, exc_val, exc_tb) become (exctype, value, traceback), sys._getframe's `offset` becomes `depth`, sys.intern's `s` becomes `string`, and sys.settrace's `tracefunc` becomes `function`. sys._clear_type_descriptors takes the name CPython gives it, which Rust spells r#type. Assisted-by: Claude Code:claude-opus-5

deque.rotate's `mid` becomes `n`, deque.extend's `iter` becomes `iterable`, _sre.ascii_tolower's `ch` becomes `character`, _operator.neg's `pos` becomes `a`, signal.alarm's `time` becomes `seconds`, and codecs.register_error's `name` becomes `errors`. gc.collect and charmap_build keep theirs. Their argument is a FromArgs struct or a PosArgs bundle, so the reported name is the binding rather than a parameter, and renaming the binding would only disguise that. Assisted-by: Claude Code:claude-opus-5

unicodedata.category's `character` becomes `chr`, math.isqrt's `x` becomes `n`, cmath.polar's `x` becomes `z`, struct.calcsize's `fmt` becomes `format`, binascii.crc32's `init` becomes `crc`, zlib.adler32's `begin_state` becomes `value`, and array.append's `x` becomes `v`. array.fromunicode's parameter is `ustr`, which cspell has to be told about. array.__deepcopy__ keeps `_memo`, which the generator now reports as `memo`; CPython calls it `unused`, a name synthesised from METH_O rather than chosen. Assisted-by: Claude Code:claude-opus-5

CPython calls the argument of split and subgroup `matcher_value`. Assisted-by: Claude Code:claude-opus-5

syn already removes r# through IdentExt::unraw, the way from_args.rs does for a field name. The empty-name guard never ran: a bare `_` is Pat::Wild, which func_sig has already refused. Assisted-by: Claude Code:claude-fable-5-1

Actionable comments posted: 1

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Inline comments:
In `@crates/vm/src/builtins/list.rs`:
- Line 202: Rename the element parameter to object in the list.insert method
while preserving its existing behavior and all references within the method, so
the #[pymethod]-derived signature matches CPython.

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📒 Files selected for processing (31)

.cspell.json
crates/derive-impl/src/util.rs
crates/stdlib/src/array.rs
crates/stdlib/src/binascii.rs
crates/stdlib/src/cmath.rs
crates/stdlib/src/math.rs
crates/stdlib/src/pystruct.rs
crates/stdlib/src/unicodedata.rs
crates/stdlib/src/zlib.rs
crates/vm/src/builtins/bool.rs
crates/vm/src/builtins/bytearray.rs
crates/vm/src/builtins/bytes.rs
crates/vm/src/builtins/complex.rs
crates/vm/src/builtins/float.rs
crates/vm/src/builtins/int.rs
crates/vm/src/builtins/list.rs
crates/vm/src/builtins/object.rs
crates/vm/src/builtins/str.rs
crates/vm/src/builtins/tuple.rs
crates/vm/src/builtins/type.rs
crates/vm/src/exception_group.rs
crates/vm/src/stdlib/_codecs.rs
crates/vm/src/stdlib/_collections.rs
crates/vm/src/stdlib/_operator.rs
crates/vm/src/stdlib/_signal.rs
crates/vm/src/stdlib/_sre.rs
crates/vm/src/stdlib/_weakref.rs
crates/vm/src/stdlib/itertools.rs
crates/vm/src/stdlib/os.rs
crates/vm/src/stdlib/posix.rs
crates/vm/src/stdlib/sys.rs

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Merging this PR will degrade performance by 12.1%

❌ 1 regressed benchmark
✅ 65 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	gc_traversal.py[rustpython]	688.1 ms	782.8 ms	-12.1%

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Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

Comparing leehanjeong:8383-cpython-param-names (c9ffb1d) with main (3191eca)

CPython also falls back to these names for METH_O, but list.append and insert, set.add, discard and remove, _weakref.getweakrefcount and getweakrefs, sys.displayhook and getrefcount, and array.__deepcopy__ get them from an Argument Clinic signature. The earlier commit that kept array.__deepcopy__'s `_memo` was wrong to call `unused` synthesised. test_pydoc's set.add summary-line tests now pass. Assisted-by: Claude Code:claude-opus-5

Thank you so much! looking everything is going great!

@youknowone BTW, CPython fills in object from METH_O when a docstring has no signature of its own (typeobject.c):

case METH_O:
    return "($self, object, /)";
case METH_O|METH_CLASS:
    return "($type, object, /)";

dict.__class_getitem__ (dictobject.c) and _stat.S_IMODE (docstring, registration) are such functions, so the object they report is this placeholder rather than a name anyone chose. This PR only followed chosen names, so it didn't rename RustPython's args and mode. test_pydoc checks the placeholder, though:

RustPython/Lib/test/test_pydoc/test_pydoc.py

Lines 1588 to 1597 in 3191eca

    
           @unittest.expectedFailure  # TODO: RUSTPYTHON 
        
           def test_module_level_callable_o(self): 
        
               try: 
        
                   import _stat 
        
               except ImportError: 
        
                   # stat.S_IMODE() and _stat.S_IMODE() have a different signature 
        
                   self.skipTest('_stat extension is missing') 
        
               self.assertEqual(self._get_summary_line(_stat.S_IMODE), 
        
                   "S_IMODE(object, /)")

RustPython/Lib/test/test_pydoc/test_pydoc.py

Lines 1636 to 1644 in 3191eca

    
           @unittest.expectedFailure  # TODO: RUSTPYTHON 
        
           def test_unbound_builtin_classmethod_o(self): 
        
               self.assertEqual(self._get_summary_line(dict.__dict__['__class_getitem__']), 
        
                   "__class_getitem__(type, object, /) unbound builtins.dict method") 
        
           @unittest.expectedFailure  # TODO: RUSTPYTHON 
        
           def test_bound_builtin_classmethod_o(self): 
        
               self.assertEqual(self._get_summary_line(dict.__class_getitem__), 
        
                   "__class_getitem__(object, /) class method of builtins.dict")

Renaming the parameter to object in the 35 __class_getitem__ definitions that take a single argument and in the 13 _stat functions would fix these three tests. About 50 other METH_O placeholders, such as slice.indices and socket.bind, have no test checking them, so I'd leave those alone either way. Should I send a follow-up PR for the rename, or keep the current names?

one of my idea is integrating docstring comparison to whatsleft.py, which currently only check existence.
How about starting from there? Then what do you suggest as next step?

Oh, I didn't know about whats_left.py. Good idea. If I fix it first, we can measure everything in one consistent way. I'll start with that.

When I took a look at the code, signatures and docstrings are skipped for native functions and methods, unlike Python-defined functions and classes. (related to cc2c46b (2021, #2410))

Two more things I'd fix on the way:

Docstring mismatches are dropped for a module that has no missing items and no signature mismatches. annotationlib is one.
A builtin type method with a different signature is reported as missing, not as different.

Then the script alone can track later signature work.

I have two questions:

Should the script also look inside classes in native modules, like _io.TextIOWrapper and _collections.deque? Right now it only looks inside the fixed list of builtin types. But most native signatures are methods of such classes. I counted 2,226 class methods and only 961 module-level functions.
For the METH_O placeholder object from my earlier question: is it fine to just report it as a difference for now? Python can't tell a placeholder from a real name, so the script can't treat it specially anyway. We can decide later whether RustPython should use object too.

After that, I suggest these next steps, in order:

FromArgs: the generator can't see inside a FromArgs struct, so several parameters collapse into one name. For example str.split shows ($self, args, /) but CPython shows ($self, /, sep=None, maxsplit=-1), and os.stat shows (path, dir_fd, follow_symlinks, /) but CPython shows (path, *, dir_fd=None, follow_symlinks=True). This is the biggest remaining gap, and it also needs * for keyword-only parameters and default values.
PosArgs: a PosArgs parameter is printed as a single parameter. For example set.union shows ($self, others, /) but CPython shows ($self, /, *others).
Types: almost no class has a __text_signature__ yet (4 of 419 native types, while CPython has it on 83), so inspect.signature(list) fails with "no signature found".

about questions,

Let's try and see what's happening. that sounds like a good idea.
Sure, your suggestion is reasonable.

About FromArgs, can we add a method to FromArgs to support those behavior? When binding arguments, we expand multiple args into FromArgs fields. Then I feel like the natural way is the signature also can be expanded from FromArgs.

PosArgs handling will be trivial. types __text_signature__ is a good point, thanks. I didn't know that 👍

github-actions Bot added the z-ca-2026 Tag to track Contribution Academy 2026 label Sep 17, 2026

github-actions Bot assigned leehanjeong Sep 17, 2026

leehanjeong added 7 commits September 17, 2026 12:47

Name BaseExceptionGroup.split's parameter the way CPython names it

26183fb

CPython calls the argument of split and subgroup `matcher_value`. Assisted-by: Claude Code:claude-opus-5

leehanjeong force-pushed the 8383-cpython-param-names branch from ab108d3 to 26183fb Compare September 17, 2026 03:48

leehanjeong marked this pull request as ready for review September 17, 2026 08:46

coderabbitai Bot reviewed Sep 17, 2026

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Comment thread crates/vm/src/builtins/list.rs Outdated

youknowone approved these changes Sep 17, 2026

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youknowone merged commit df653ce into RustPython:main Sep 17, 2026
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leehanjeong mentioned this pull request Sep 20, 2026

Compare native signatures and docstrings in whats_left.py #8751

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Name generated signature parameters the way CPython names them by leehanjeong · Pull Request #8725 · RustPython/RustPython · GitHub

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Name generated signature parameters the way CPython names them by leehanjeong · Pull Request #8725 · RustPython/RustPython · GitHub

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Name generated signature parameters the way CPython names them#8725youknowone merged 9 commits intoRustPython:mainRustPython/RustPython:mainfrom leehanjeong:8383-cpython-param-namesleehanjeong/RustPython:8383-cpython-param-namesCopy head branch name to clipboard

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Left for #8383

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