模拟 class 方法，仍然运行带有一些包装代码的原始方法

Question

我想通过运行原始方法在前后添加代码来修补一个方法。特别是，我在 pyfakefs 内存文件系统中进行了运行测试，但有时我想使用真实的文件系统，因为某些软件包无法在假文件系统上运行 (pybedtools 在我的例子中）。

可能有一个简单的方法可以做到这一点，但我尝试了很多很多次后还是无法弄清楚。这可能吗？

举个例子，下面我试图在 pandas 中修补 to_csv。

import os
import tempfile
from unittest.mock import patch
import pandas as pd
from pyfakefs.fake_filesystem_unittest import Patcher


df_intervals = pd.DataFrame([
     ['1', 10, 20],
     ['20', 45, 55]],
     columns=['chrom', 'start', 'end'])


with Patcher(use_known_patches=True) as patcher:
    # As expecte writing to fake filesystem works
    fname = tempfile.NamedTemporaryFile()
    df_intervals.to_csv(fname.name)
    assert not os.path.exists(fname.name)
    assert patcher.fs.isfile(fname.name)

    # But, how do I patch `to_csv` to write to the real filesystem? My failed attempts:
    # Attempt 1
    # TypeError: super(type, obj): obj must be an instance or subtype of type
    class patched_DataFrame(pd.DataFrame):
        def to_csv(self, fname):
            print('Pausing fake file system')
            patcher.pause()
            super().to_csv(fname)
            print('Resuming fake file system')
            patcher.resume()

    with patch.object(pd.core.generic.NDFrame, 'to_csv', new=patched_DataFrame.to_csv):
        df_intervals.to_csv(fname.name)

    # Attempt 2: TypeError: 'patched_DataFrame' object is not callable
    with patch('pandas.core.frame.DataFrame', new_callable=patched_DataFrame):
        df_intervals.to_csv(fname.name)

    # Attempt 3: infinite recursion
    def patched_to_csv(self, fname):
        print('Pausing fake file system')
        patcher.pause()
        self.to_csv(fname)
        print('Resuming fake file system')
        patcher.resume()

    with patch.object(pd.core.generic.NDFrame, 'to_csv', new=patched_to_csv):
        df_intervals.to_csv(fname.name)

Answer 1

一种（不是很优雅）的可能性是使用第三种方法并通过使用旧保存的 to_csv 方法避免递归：

from pyfakefs.fake_filesystem_unittest import Patcher, Pause


with Patcher() as patcher:
    ...

    def patched_to_csv(self, fname):
        with Pause(patcher.fs):
            original_to_csv(self, fname)

    original_to_csv = pd.core.generic.NDFrame.to_csv
    with patch.object(pd.core.generic.NDFrame, 'to_csv', new=patched_to_csv):
        df_intervals.to_csv(fname.name)

请注意，我为 pause/resume 使用了上下文管理器 - 这将允许在需要时轻松传播补丁函数的 return 值并且不易出错。
另请注意 use_known_patches 默认为 True。

免责声明:
我是 pyfakefs.

的贡献者

更新：我修改了答案，因为之前试图避免递归的尝试是错误的。

Answer 2

这是一种方法。

df_intervals = pd.DataFrame([
     ['1', 10, 20],
     ['20', 45, 55]],
     columns=['chrom', 'start', 'end'])


def fakefs_decorator(func, patcher):
    """ Force a method to work on the real filesystem """
    def fs_wrapper(*args, **kwargs):
        patcher.pause()
        out = func(*args, **kwargs)
        patcher.resume()
        return out

    if hasattr(func, '__self__'):
        def c_wrapper(_, *args, **kwargs):
            return fs_wrapper(*args, **kwargs)
        return classmethod(c_wrapper)
    return fs_wrapper


with Patcher(allow_root_user=False, use_known_patches=True) as patcher:
    fs_from_dataframe = fakefs_decorator(pybedtools.BedTool.from_dataframe, patcher)
    fs_to_dataframe = fakefs_decorator(pybedtools.BedTool.to_dataframe, patcher)
    fs_intersect = fakefs_decorator(pybedtools.BedTool.intersect, patcher)

    @patch('pybedtools.BedTool.from_dataframe', new=fs_from_dataframe)
    @patch('pybedtools.bedtool.BedTool.to_dataframe', new=fs_to_dataframe)
    @patch('pybedtools.bedtool.BedTool.intersect', new=fs_intersect)
    def test(df_intervals):
        bed_object = pybedtools.BedTool.from_dataframe(df_intervals)
        joined_bed_object = bed_object.intersect(bed_object)
        df = joined_bed_object.to_dataframe()
        return df

    df = test(df_intervals)

模拟 class 方法，仍然运行带有一些包装代码的原始方法

Mocking class methods, still running the original method with some wrapped code

python

pandas

testing

mocking

pyfakefs

模拟 class 方法，仍然 运行 带有一些包装代码的原始方法

Mocking class methods, still running the original method with some wrapped code

python

pandas

testing

mocking

pyfakefs

模拟 class 方法，仍然运行带有一些包装代码的原始方法