bytearray.take_bytes() accepts negative n and raises BufferError with memoryview - both undocumented

[zhouxjpypl]

Bug report

Bug description:

Python 3.15.0a8 bytearray.take_bytes() Test Report

Test Environment

• Python Version: 3.15.0a8
• Compiler: Clang 13.0.0 (clang-1300.0.29.30)
• Operating System: macOS (Darwin)
• Test Date: 2026-04-18

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Issues Found

Issue 1: Negative Argument Behavior Is Undocumented

Description

The bytearray.take_bytes(n) method accepts negative values for n. When a negative value is provided, the behavior is equivalent to take_bytes(len(ba) + n), similar to Python slice semantics. However, this behavior is not documented.

Reproduction Code

ba = bytearray(b'hello')
result = ba.take_bytes(-1)
print(result)  # b'hell'
print(ba)      # bytearray(b'o')

Test Results

Input	Return Value	Remaining bytearray	Explanation
-1	b'hell'	b'o'	Takes len-1 bytes
-2	b'hel'	b'lo'	Takes len-2 bytes
-3	b'he'	b'llo'	Takes len-3 bytes
-4	b'h'	b'ello'	Takes len-4 bytes
-5	b''	b'hello'	Takes 0 bytes
-6	IndexError	-	Out of range

Expected Behavior

Option A: Document the negative argument behavior explicitly
Option B: Reject negative values and raise ValueError

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Issue 2: BufferError Raised When Active memoryview Exists

Description

When there is an active memoryview reference to the bytearray, calling take_bytes() raises a BufferError. This limitation is not documented.

Reproduction Code

ba = bytearray(b'12345')
mv = memoryview(ba)
ba.take_bytes(3)  # BufferError: Existing exports of data: object cannot be re-sized

Test Results

Scenario	Result
Active memoryview exists	BufferError
After releasing memoryview	Works normally
Multiple memoryviews exist	BufferError

Expected Behavior

Option A: Document this limitation in the official documentation
Option B: Make take_bytes() work even when memoryview references exist (e.g., create a copy instead of in-place modification)

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Expected vs Actual Behavior Summary

Scenario	Expected Behavior	Actual Behavior	Status
take_bytes(-1)	Should be documented	Slice-like behavior	⚠️ Undocumented
Negative n out of range	Should be documented	IndexError	⚠️ Undocumented
Call with active memoryview	Should be documented	BufferError	⚠️ Undocumented

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Recommendations

1. Update Documentation: Add the following to the bytearray.take_bytes() documentation:

   • Explanation of negative argument behavior
   • Note about the limitation with memoryview references

2. Or Change Behavior:

   • Reject negative arguments (raise ValueError)
   • Make take_bytes() compatible with active memoryview references

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Attachments

• Test script: test_take_bytes_negative_detail.py
• Test script: test_memoryview.py

CPython versions tested on:

3.15

Operating systems tested on:

macOS