wave.open fails on non-seekable input streams that implement tell()

[augusto-rehfeldt]

Bug report

Bug description:

Documented behaviour: The wave module's opening documentation states: "When the setpos() and rewind() methods are not used, the seek() method is not necessary."

Expected: Opening succeeds; sequential reads return (b'', b'\xce', b'$', b'', b'').

Actual: AttributeError: 'Stream' object has no attribute 'seek'

import struct
import wave

wav = b'RIFF&\x00\x00\x00WAVEfmt \x10\x00\x00\x00\x01\x00\x01\x00@\x1f\x00\x00@\x1f\x00\x00\x01\x00\x08\x00data\x02\x00\x00\x00\xce$'
requests = (0, 1, 2, 3, 1)

class Stream:
    def __init__(self):
        self.pos = 0
    def read(self, n=-1):
        end = len(wav) if n < 0 else min(len(wav), self.pos + n)
        data = wav[self.pos:end]
        self.pos = end
        return data
    def tell(self):
        return self.pos
    def close(self):
        pass

def main():
    try:
        fields = struct.unpack('<4sI4s4sIHHIIHH4sI2s', wav)
        valid = fields == (
            b'RIFF', len(wav) - 8, b'WAVE', b'fmt ', 16,
            1, 1, 8000, 8000, 1, 8, b'data', 2, b'\xce$'
        )
    except struct.error:
        valid = False
    if not valid:
        print('REFUTATION REJECTED:', 'input is not the complete PCM WAV claimed')
        return

    audio = fields[-1]
    pos = 0
    chunks = []
    for n in requests:
        chunks.append(audio[pos:pos + n])
        pos = min(len(audio), pos + n)
    expected = ('ok', (1, 1, 8000, len(audio), 'NONE', 'not compressed'),
                tuple(chunks))
    try:
        with wave.open(Stream(), 'rb') as reader:
            actual = ('ok', tuple(reader.getparams()),
                      tuple(reader.readframes(n) for n in requests))
    except Exception as exc:
        actual = ('exception', type(exc).__name__, str(exc))

    if actual != expected:
        print('REFUTATION CONFIRMED:',
              {'wav': wav, 'read_requests': requests},
              'actual:', actual, 'expected:', expected)
    else:
        print('REFUTATION REJECTED:', 'sequential reading matches the documented expectation')

main()

Output on Python 3.14.6 (Windows-11-10.0.26220-SP0), standard library wave:

REFUTATION CONFIRMED: {'wav': b'RIFF&\x00\x00\x00WAVEfmt \x10\x00\x00\x00\x01\x00\x01\x00@\x1f\x00\x00@\x1f\x00\x00\x01\x00\x08\x00data\x02\x00\x00\x00\xce$', 'read_requests': (0, 1, 2, 3, 1)} actual: ('exception', 'AttributeError', "'Stream' object has no attribute 'seek'") expected: ('ok', (1, 1, 8000, 2, 'NONE', 'not compressed'), (b'', b'\xce', b'$', b'', b''))

This report was found and written by an automated property-testing tool I run (bugforge). The reproducer above was executed and its output is pasted unedited; no person reviewed the report before it was filed. The search script is in https://github.com/augusto-rehfeldt/bugforge-results/tree/main/wave-20261003-182548-c1

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ZeroIntensity]

See #158748 (comment).