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`hasattr(stream, "buffer") fails with ValueError if buffer is detached

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  • ¿Algo no está bien?
#160,427 3 comentarios 0 reacciones 0 asignados Ver en GitHub

Los mantenedores suelen responder en 1 día

Nadie ha tomado este issue todavía.

  • #160467 de @scrieve — cerrado sin fusionar

Evaluación

Dificultad
3/5
Tiempo estimado
1-2 días
Aptitud para principiantes
35/100
Tipo de issue
Error
Claridad
Bastante claro
Estado de actividad
Estancado
Stack tecnológico
python
Área
backend

Línea de trabajo

Start by reading the linked pull request #160467 and the stream buffer property implementation and related tests it identifies. Reproduce the detached-buffer example in the issue on the affected Python versions, then use the relevant tests to confirm hasattr(stream, "buffer") no longer raises ValueError after detachment.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

extension-modules topic-IO type-bug
Bug report
>>> stream  =  open("example.txt", "w")
>>> hasattr(stream, "buffer")
True
>>> stream.detach()
<_io.BufferedWriter name='example.txt'>
>>> hasattr(stream, "buffer")
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    hasattr(stream, "buffer")
    ~~~~~~~^^^^^^^^^^^^^^^^^^
ValueError: underlying buffer has been detached

This occurs with Python 3.14.9 and 3.15.1, but not with earlier versions such as 3.14.8 and 3.15.0. Tested both on Linux and on Windows. I consider hasattr failing with an exception pretty bad, especially when using it with standard library objects, and the behavior changing in a bug fix release makes it even worse.

I noticed this when a unit test for our custom isatty utility started to fail (https://github.com/robotframework/robotframework/issues/5825). We have that utility so that we can safely check is a stream connected to console or not. It used to look like this:

def isatty(stream):
    # first check if buffer was detached
    if hasattr(stream, "buffer") and stream.buffer is None:
        return False
    if not hasattr(stream, "isatty"):
        return False
    try:
        return stream.isatty()
    except ValueError:  # Occurs if file is closed.
        return False

I already fixed this in our end by simply removing the separate detached buffer check. stream.isatty() raised a ValueError if its buffer is detached, similarly when the stream is closed, and we already handle that. Apparently the separate check was added before handling closed streams and nobody noticed earlier that the check is redundant.

CPython versions tested on:

3.14, 3.15

Operating systems tested on:

Linux, Windows

Linked PRs
  • gh-160467
Lenguaje dominante
Python
Estrellas
77.7k
Forks
38.3k
Merge medio
13 h 43 min
PR fusionados (30 d)
704

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