wave.Wave_write.setparams() rejects valid PCM-to-IEEE-float parameter changes #160030

Bug report

Bug description

wave.Wave_write.setparams() rejects valid IEEE-float parameters when the writer was previously configured with a PCM sample width of 1, 2, or 3 bytes, even though no audio frames have been written.

The same parameters succeed on a fresh writer.

Reproducer

import io
import wave

float_params = (
    1, 4, 8000, 0, "NONE", "not compressed",
    wave.WAVE_FORMAT_IEEE_FLOAT,
)

with wave.open(io.BytesIO(), "wb") as writer:
    writer.setparams(float_params)
    print("Fresh writer: OK")

with wave.open(io.BytesIO(), "wb") as writer:
    writer.setparams((1, 2, 8000, 0, "NONE", "not compressed"))
    writer.setparams(float_params)
    print("Reconfigured writer: OK")

Actual behavior

The fresh-writer configuration succeeds. Reconfiguring the PCM writer raises:

wave.Error: unsupported sample width for IEEE float format

Expected behavior

Both configurations should succeed. The new sample width is 4 bytes, which is supported for IEEE float, and no frames have been written.

Implementation details

Wave_write.setparams() calls setformat(format) before
setsampwidth(sampwidth).

However, setformat() validates the existing self._sampwidth against the
new format. This rejects the previous 2-byte PCM width before the valid
new 4-byte width can be installed.

The same failure occurs when switching from PCM widths of 1, 2, or 3 bytes
to either 4-byte or 8-byte IEEE float. Switching from 4-byte PCM succeeds.

Related: #60729 added IEEE-float support.

CPython versions tested on

Python 3.16.0a1+dev, debug build based on commit 8b7d6c53eee.

Also reproduced using Lib/wave.py from upstream commit
f5bd07700ecd0f02cc424666b871f51de03b9232, executed under Python 3.14.8.
This additional check was not a full build of that upstream commit.

Operating systems tested on

macOS

Output from running python -VV

Python 3.16.0a1+dev (heads/gh-159868-userstring-affixes-dirty:8b7d6c53eee, Oct 20 2026, 15:46:41) [Clang 21.0.0 (clang-2100.3.34.2)]

CPython versions tested on:

3.16

Operating systems tested on:

macOS

Linked PRs

• gh-160030: Validate wave format and sample width together in setparams #160031