扩展 scipy.stats.rv_continuous 时的元类错误为 Read the Docs 嘲笑

Question

在我的 Python 项目中，我像这样扩展 scipy.stats.rv_continuous：

class GenlogisticGen(LmomDistrMixin, scipy.stats.rv_continuous):
    ...

我正在尝试在 Read the Docs 上构建文档，但遇到构建错误：

class GenlogisticGen(LmomDistrMixin, scipy.stats.rv_continuous):
TypeError: metaclass conflict: the metaclass of a derived class must
be a (non-strict) subclass of the metaclasses of all its bases

请注意，我根据 Read the Docs FAQ 模拟了 scipy.stats 模块。

我猜想通过模拟基类会出现问题。但是什么？

Answer 1

我今天遇到了同样的问题，但是是 Qt 相关的课程。问题是 ReadTheDocs 建议的 Mock 类具有与预期不同的元类。这是问题的描述和解决方案，您想要的是从object继承的基类：

# =============================================================================
# Part 1. Set up the mock (you would put this in conf.py for Sphinx/autodoc).
# =============================================================================

import os
import sys
from unittest.mock import MagicMock


class Mock(MagicMock):
    """
    Mock class that gives whatever attribute it's asked for, as per
    https://docs.readthedocs.io/en/latest/faq.html. Intended to be used when
    you can't genuinely install/import a module because ReadTheDocs (RTD)
    doesn't allow the installation of modules with C (rather than pure Python)
    code.
    """
    @classmethod
    def __getattr__(cls, name: str):
        return MagicMock()


class SimpleClass(object):
    """
    Dummy base class to replace a :class:`Mock` version; see
    ``FIX_THE_PROBLEM`` below.
    """
    pass


MOCK_MODULES = [
    # Things that ReadTheDocs won't install, but we want:
    'PyQt5',
    'PyQt5.QtCore',
    'PyQt5.QtGui',
    'PyQt5.QtNetwork',
    'PyQt5.QtWidgets',
]

ON_READTHEDOCS = os.environ.get('READTHEDOCS') == 'True'  # the normal test
ON_READTHEDOCS = True  # for testing!
if ON_READTHEDOCS:
    # Insert copies of our Mock class for modules we want to fake.
    sys.modules.update((mod_name, Mock()) for mod_name in MOCK_MODULES)


MODULE_MEMBERS_TO_MAKE_SIMPLE_CLASS = (
    ('PyQt5.QtCore', 'QAbstractListModel'),
    ('PyQt5.QtCore', 'QAbstractTableModel'),
    # etc.
)


FIX_THE_PROBLEM = False  # to see the problem, or True to fix it!
if FIX_THE_PROBLEM:
    for module_name, class_name in MODULE_MEMBERS_TO_MAKE_SIMPLE_CLASS:
        setattr(sys.modules[module_name], class_name, SimpleClass)


# =============================================================================
# Part 2. Simulate some user code.
# =============================================================================

from PyQt5.QtCore import QAbstractListModel

print(QAbstractListModel)
# For real:                 <class 'PyQt5.QtCore.QAbstractListModel'>
# If ON_READTHEDOCS:        <MagicMock id='139789117901176'>
# If FIX_THE_PROBLEM too:   <class '__main__.SimpleClass'>

print(type(QAbstractListModel))
# For real:                 <class 'sip.wrappertype'>
# If ON_READTHEDOCS:        <class 'unittest.mock.MagicMock'>
# If FIX_THE_PROBLEM too:   <class 'type'>


class MyRandomMixin(object):
    pass


class MyDerived(QAbstractListModel, MyRandomMixin):
    pass

# For real: it's happy.
# If ON_READTHEDOCS: will not create MyDerived; will crash with:
#   TypeError: metaclass conflict: the metaclass of a derived class must be a
#   (non-strict) subclass of the metaclasses of all its bases
# If ON_READTHEDOCS and FIX_THE_PROBLEM: happy again.