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Unexpected SystemError in Python3.12.0a7: <method 'startswith' of 'str' objects> returned a result with an exception set #103632

Closed as not planned
Closed as not planned
Unexpected SystemError in Python3.12.0a7: <method 'startswith' of 'str' objects> returned a result with an exception set#103632
Labels
type-bugAn unexpected behavior, bug, or error

Description

@abravalheri
abravalheri
opened on Apr 19, 2023

Bug report

I noticed recently that Setuptools CI started failing for Python 3.12.0a7 with a SystemError that is difficult to understand:

SystemError: <built-in method startswith of str object at 0x7fe399991298> returned a result with an exception set

At a first glance this error does not make much sense because str.startswith is a built-in method in a built-in data structure. I am struggling to see how it can have an exception set attached to the result.

I managed to create the following simplified reproducer:

docker run --rm -it python:3.12.0a7-bullseye
Python 3.12.0a7 (main, Apr 12 2023, 14:13:09) [GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> class Distribution:
...     @property
...     def version(self):
...         try:
...             return self._version
...         except AttributeError as e:
...             # ... complex code omitted for the sake of simplification ...
...             raise ValueError("Missing Version")
...     def __getattr__(self, attr):
...         if attr.startswith("_"):
...             raise AttributeError(attr)
...         # ... complex code omitted for the sake of simplification ...
...         return 42
...
>>> dist = Distribution()
>>> dist.version
Traceback (most recent call last):
  File "<stdin>", line 5, in version
  File "<stdin>", line 11, in __getattr__
AttributeError: _version. Did you mean: 'version'?

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 8, in version
ValueError: Missing Version

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 10, in __getattr__
SystemError: <method 'startswith' of 'str' objects> returned a result with an exception set
>>>

The error seems to be related to the combination of the following factors:

  1. A property is being used1
  2. The property getter access an undefined attribute and triggers __getattr__
  3. __getattr__ raises an AttributeError
  4. The property getter is supposed to catch the AttributeError exception and raise a different exeception.

My expectation is that the SystemError never gets triggered with the confusing message. Instead the example should end up with a ValueError.

Please note that the example is very simplified. For the realistic implementation please consider pkg_resources.Distribution.

Your environment

  • CPython versions tested on: 3.12.0a7
  • Operating system and architecture:
    Reproducer tested on both Ubuntu 20.04.6 LTS machine and python:3.12.0a7-bullseye container

Problem also identified in GitHub Actions runners: ubuntu-latest, macos-latest, windows-latest (see https://github.com/pypa/setuptools/actions/runs/4710601389?pr=3893) for Python 3.12-dev.

Footnotes

  1. If we replace the property with a regular method, the example works as expected. ↩

Activity

  1. abravalheri
    added
    type-bugAn unexpected behavior, bug, or error
    on Apr 19, 2023

  2. sunmy2019 commented on Apr 20, 2023

    @sunmy2019
    sunmy2019
    on Apr 20, 2023
    Member

    It should be fixed by #103332

  3. sobolevn commented on Apr 21, 2023

    @sobolevn
    sobolevn
    on Apr 21, 2023
    Member

    I agree that this should be fixed in main. Please, reopen if it is not fixed.

  4. sobolevn
    closed this as not plannedon Apr 21, 2023

  5. abravalheri commented on Apr 21, 2023

    @abravalheri
    abravalheri
    on Apr 21, 2023
    Author

    Thank you very much.

    I run the test above with an adapted Dockerfile that gets the latest `main` and it seems to work 
    FROM buildpack-deps:bullseye

# ensure local python is preferred over distribution python
ENV PATH /usr/local/bin:$PATH

# http://bugs.python.org/issue19846
# > At the moment, setting "LANG=C" on a Linux system *fundamentally breaks Python 3*, and that's not OK.
ENV LANG C.UTF-8

# runtime dependencies
RUN set -eux; \
    apt-get update; \
    apt-get install -y --no-install-recommends \
        libbluetooth-dev \
        tk-dev \
        uuid-dev \
    ; \
    rm -rf /var/lib/apt/lists/*

ENV PYTHON_VERSION 3.12.0dev+3e0fec7


RUN set -eux; \
    \
    wget -O /tmp/python.tar.gz "https://github.com/python/cpython/tarball/3e0fec7e07a71bdeeab7554e980110fbc47763b9"; \
    mkdir -p /usr/src/python; \
    tar --extract --directory /usr/src/python --strip-components=1 --file /tmp/python.tar.gz; \
    rm /tmp/python.tar.gz; \
    \
    cd /usr/src/python; \
    gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)"; \
    ./configure \
        --build="$gnuArch" \
        --enable-loadable-sqlite-extensions \
        --enable-optimizations \
        --enable-option-checking=fatal \
        --enable-shared \
        --with-lto \
        --with-system-expat \
        --without-ensurepip \
    ; \
    nproc="$(nproc)"; \
    EXTRA_CFLAGS="$(dpkg-buildflags --get CFLAGS)"; \
    LDFLAGS="$(dpkg-buildflags --get LDFLAGS)"; \
    make -j "$nproc" \
        "EXTRA_CFLAGS=${EXTRA_CFLAGS:-}" \
        "LDFLAGS=${LDFLAGS:-}" \
        "PROFILE_TASK=${PROFILE_TASK:-}" \
    ; \
# https://github.com/docker-library/python/issues/784
# prevent accidental usage of a system installed libpython of the same version
    rm python; \
    make -j "$nproc" \
        "EXTRA_CFLAGS=${EXTRA_CFLAGS:-}" \
        "LDFLAGS=${LDFLAGS:--Wl},-rpath='\$\$ORIGIN/../lib'" \
        "PROFILE_TASK=${PROFILE_TASK:-}" \
        python \
    ; \
    make install; \
    \
# enable GDB to load debugging data: https://github.com/docker-library/python/pull/701
    bin="$(readlink -ve /usr/local/bin/python3)"; \
    dir="$(dirname "$bin")"; \
    mkdir -p "/usr/share/gdb/auto-load/$dir"; \
    cp -vL Tools/gdb/libpython.py "/usr/share/gdb/auto-load/$bin-gdb.py"; \
    \
    cd /; \
    rm -rf /usr/src/python; \
    \
    find /usr/local -depth \
        \( \
            \( -type d -a \( -name test -o -name tests -o -name idle_test \) \) \
            -o \( -type f -a \( -name '*.pyc' -o -name '*.pyo' -o -name 'libpython*.a' \) \) \
        \) -exec rm -rf '{}' + \
    ; \
    \
    ldconfig; \
    \
    python3 --version

CMD ["python3"]

    Ref: https://github.com/docker-library/python/blob/cb6ecdbcbc7e30a180481a9911f5f1f470b9dba1/3.12-rc/bullseye/Dockerfile

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