Implement `bytearray.__str__` && `bytes.__str__` by moreal · Pull Request #7477 · RustPython/RustPython

moreal · 2026-03-20T16:43:06Z

This pull request let bytearray.__str__ and bytes.__str__ make warning. With -b or -bb option, it will show or raise warning.

Behavior changes

CPython (3.14.3)

$ python3
Python 3.14.3 (main, Feb  3 2026, 15:32:20) [Clang 17.0.0 (clang-1700.6.3.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> str(bytes.fromhex(b'aa'))
"b'\\xaa'"
>>> str(bytearray.fromhex(b'aa'))
"bytearray(b'\\xaa')"

$ python3 -b
Python 3.14.3 (main, Feb  3 2026, 15:32:20) [Clang 17.0.0 (clang-1700.6.3.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> str(bytes.fromhex(b'aa'))
<python-input-0>:1: BytesWarning: str() on a bytes instance
"b'\\xaa'"
>>> str(bytearray.fromhex(b'aa'))
<python-input-1>:1: BytesWarning: str() on a bytearray instance
"bytearray(b'\\xaa')"

RustPython (before)

$ cargo run
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s
     Running `target/debug/rustpython`
Welcome to the magnificent Rust Python 0.5.0 interpreter 😱 🖖
RustPython 3.14.0
Type "help", "copyright", "credits" or "license" for more information.
>>>>> str(bytes.fromhex(b'aa'))
"b'\\xaa'"
>>>>> str(bytearray.fromhex(b'aa'))
"bytearray(b'\\xaa')"

$ cargo run -- -b
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s
     Running `target/debug/rustpython -b`
Welcome to the magnificent Rust Python 0.5.0 interpreter 😱 🖖
RustPython 3.14.0
Type "help", "copyright", "credits" or "license" for more information.
>>>>> str(bytes.fromhex(b'aa'))
"b'\\xaa'"
>>>>> str(bytearray.fromhex(b'aa'))
"bytearray(b'\\xaa')"

RustPython (after)

$ cargo run
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s
     Running `target/debug/rustpython`
Welcome to the magnificent Rust Python 0.5.0 interpreter 😱 🖖
RustPython 3.14.0
Type "help", "copyright", "credits" or "license" for more information.
>>>>> str(bytes.fromhex(b'aa'))
"b'\\xaa'"
>>>>> str(bytearray.fromhex(b'aa'))
"bytearray(b'\\xaa')"

$ cargo run -- -b
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s
     Running `target/debug/rustpython -b`
Welcome to the magnificent Rust Python 0.5.0 interpreter 😱 🖖
RustPython 3.14.0
Type "help", "copyright", "credits" or "license" for more information.
>>>>> str(bytes.fromhex(b'aa'))
<stdin>:1: BytesWarning: str() on a bytes instance
"b'\\xaa'"
>>>>> str(bytearray.fromhex(b'aa'))
<stdin>:1: BytesWarning: str() on a bytearray instance
"bytearray(b'\\xaa')"

CPython reference

bytes.__str__ https://github.com/python/cpython/blob/v3.14.3/Objects/bytesobject.c#L1423-L1433

static PyObject *
bytes_str(PyObject *op)
{
    if (_Py_GetConfig()->bytes_warning) {
        if (PyErr_WarnEx(PyExc_BytesWarning,
                         "str() on a bytes instance", 1)) {
            return NULL;
        }
    }
    return bytes_repr(op);
}

bytearray.__str__ https://github.com/python/cpython/blob/v3.14.3/Objects/bytearrayobject.c#L1171-L1181

static PyObject *
bytearray_str(PyObject *op)
{
    if (_Py_GetConfig()->bytes_warning) {
        if (PyErr_WarnEx(PyExc_BytesWarning,
                         "str() on a bytearray instance", 1)) {
                return NULL;
        }
    }
    return bytearray_repr(op);
}

Summary by CodeRabbit

New Features
- Added string conversion for bytes and bytearray objects so str() returns a user-readable representation.
- Added a configurable warning that notifies when converting bytes/bytearray to strings (can be enabled or disabled in settings).

coderabbitai · 2026-03-20T16:43:16Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: dfe6059b-71e8-47c0-a20c-0665a7ec429d

📥 Commits

Reviewing files that changed from the base of the PR and between 08fbe7a and 590e514.

📒 Files selected for processing (2)

crates/vm/src/builtins/bytearray.rs
crates/vm/src/builtins/bytes.rs

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

crates/vm/src/builtins/bytes.rs
crates/vm/src/builtins/bytearray.rs

📝 Walkthrough

Walkthrough

Added slot_str implementations for PyBytes and PyByteArray that emit a conditional bytes_warning and return a string representation; introduced PyBytesInner::warn_on_str to centralize the warning logic.

Changes

Cohort / File(s)	Summary
Byte `__str__` slots `crates/vm/src/builtins/bytes.rs`, `crates/vm/src/builtins/bytearray.rs`	Added `#[pyslot] fn slot_str(...)` for `PyBytes` and `PyByteArray` to call the warning helper and produce the `str()`/`PyStr` representation.
Bytes warning helper `crates/vm/src/bytes_inner.rs`	Added `pub(crate) fn warn_on_str(message: &'static str, vm: &VirtualMachine) -> PyResult<()>` which conditionally emits `bytes_warning` based on VM config.

Sequence Diagram

sequenceDiagram
    participant Caller
    participant PyObj as PyBytes / PyByteArray
    participant Inner as PyBytesInner
    participant VM as VirtualMachine
    participant Config as VM Config

    Caller->>PyObj: str(obj)
    PyObj->>Inner: warn_on_str(message, vm)
    Inner->>Config: read bytes_warning
    Config-->>Inner: bytes_warning level
    alt bytes_warning > 0
        Inner->>VM: emit bytes_warning(exception, message)
    end
    Inner-->>PyObj: Ok(())
    PyObj->>PyObj: compute repr / repr_with_name
    PyObj-->>Caller: PyStr (string)

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

Add tp_str #6495 — Introduces the Str slot variant and wiring for slot-based __str__, closely related to adding slot_str implementations for bytes types.

Suggested reviewers

youknowone

Poem

🐰 I nibble bytes and spin a tale so bright,
A gentle warning springs before they speak at night.
From inner burrows to the VM's light,
Strings now hop out tidy and polite. 🥕✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 44.44% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and accurately summarizes the main changes: implementing `__str__` for both `bytearray` and `bytes` classes by adding slot implementations.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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coderabbitai

🧹 Nitpick comments (1)

crates/vm/src/builtins/bytes.rs (1)

227-231: Please add regression coverage for warning modes.

Recommend adding tests that assert:

default mode: no warning,
-b: BytesWarning emitted,
-bb: warning escalates appropriately,
while str(bytes_obj) output remains unchanged in all cases.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@crates/vm/src/builtins/bytes.rs` around lines 227 - 231, Add regression tests
for the bytes __str__ path that exercise PyBytesInner::warn_on_str via the
bytes.__str__ implementation: create a bytes object, call str(bytes_obj) and
assert its output is unchanged, then run three scenarios asserting
warnings/behavior: (1) default mode — no warning emitted; (2) warning mode "-b"
— a BytesWarning is emitted when calling str(bytes_obj); (3) warning mode "-bb"
— the warning is escalated (treated as an error) when calling str(bytes_obj).
Use the same call into the code path that triggers PyBytesInner::warn_on_str and
make explicit assertions about the presence/absence/type of warning while
keeping the returned string identical in all cases.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@crates/vm/src/builtins/bytes.rs`:
- Around line 227-231: Add regression tests for the bytes __str__ path that
exercise PyBytesInner::warn_on_str via the bytes.__str__ implementation: create
a bytes object, call str(bytes_obj) and assert its output is unchanged, then run
three scenarios asserting warnings/behavior: (1) default mode — no warning
emitted; (2) warning mode "-b" — a BytesWarning is emitted when calling
str(bytes_obj); (3) warning mode "-bb" — the warning is escalated (treated as an
error) when calling str(bytes_obj). Use the same call into the code path that
triggers PyBytesInner::warn_on_str and make explicit assertions about the
presence/absence/type of warning while keeping the returned string identical in
all cases.

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: 97d67d10-55d4-45a2-9406-15e1acf0abdc

📥 Commits

Reviewing files that changed from the base of the PR and between a1203ae and 08fbe7a.

📒 Files selected for processing (3)

crates/vm/src/builtins/bytearray.rs
crates/vm/src/builtins/bytes.rs
crates/vm/src/bytes_inner.rs

youknowone · 2026-03-21T00:45:52Z

crates/vm/src/builtins/bytearray.rs

+    #[pymethod]
+    fn __str__(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyStrRef> {


Suggested change

#[pymethod]

fn __str__(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyStrRef> {

#[pyslot]

fn slot_str(zelf: &PyObject, vm: &VirtualMachine) -> PyResult<PyStrRef> {

does this work?

Yes. I applied it in 590e514

I think it would be nice to have a trait that implements slot_str (like Representable), but I can't think of a good name for it. 😅

If you are interested in, could you also check this? #6485
That was a trial that removing single function traits. But this is a big change of interface design. I'd like to listen how other people think about it.

I left my thought on the pull request #6485 (comment)

moreal added 2 commits March 21, 2026 01:28

Implement bytearray.__str__

bfe3d8b

Implement bytes.__str__

08fbe7a

moreal marked this pull request as ready for review March 20, 2026 18:01

coderabbitai bot reviewed Mar 20, 2026

View reviewed changes

youknowone reviewed Mar 21, 2026

View reviewed changes

Turn __str__ method into slot

590e514

moreal requested a review from youknowone March 21, 2026 13:09

youknowone enabled auto-merge (squash) March 21, 2026 13:52

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Implement `bytearray.str` && `bytes.str`#7477

Implement `bytearray.str` && `bytes.str`#7477
moreal wants to merge 3 commits intoRustPython:mainfrom
moreal:missing-str

moreal commented Mar 20, 2026 •

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Walkthrough

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Sequence Diagram

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		#[pymethod]
		fn __str__(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyStrRef> {

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Behavior changes

CPython (3.14.3)

RustPython (before)

RustPython (after)

CPython reference

Summary by CodeRabbit

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Walkthrough

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moreal commented Mar 20, 2026 •

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