为什么tempfile.SpooledTemporaryFile不实现可读，可写，可搜索?

问题描述

在Python 3.6.1中，我尝试将tempfile.SpooledTemporaryFile包装在io.TextIOWrapper中:

In Python 3.6.1, I've tried wrapping a tempfile.SpooledTemporaryFile in an io.TextIOWrapper:

with tempfile.SpooledTemporaryFile() as tfh:
    do_some_download(tfh)
    tfh.seek(0)
    wrapper = io.TextIOWrapper(tfh, encoding='utf-8')
    yield from do_some_text_formatting(wrapper)

wrapper = io.TextIOWrapper(tfh, encoding='utf-8')行给我一个错误:

AttributeError: 'SpooledTemporaryFile' object has no attribute 'readable'

如果我创建像这样的简单类，则可以绕过该错误(对于writable和seekable，我也会收到类似的错误):

If I create a simple class like this, I can bypass the error (I get similar errors for writable and seekable):

class MySpooledTempfile(tempfile.SpooledTemporaryFile):
    @property
    def readable(self):
        return self._file.readable

    @property
    def writable(self):
        return self._file.writable

    @property
    def seekable(self):
        return self._file.seekable

是否有充分的理由说明tempfile.SpooledTemporaryFile不具有这些属性?

Is there a good reason why tempfile.SpooledTemporaryFile doesn't already have these attributes?

推荐答案

SpooledTemporaryFile实际上在后台使用了两种不同的_file实现-最初是io缓冲区(StringIO或BytesIO)，直到它翻滚并通过tempfile.TemporaryFile()创建一个文件状对象"(例如，当超出max_size时).

SpooledTemporaryFile actually uses 2 different _file implementations under the hood - initially an io Buffer (StringIO or BytesIO), until it rolls over and creates a "file-like object" via tempfile.TemporaryFile() (for example, when max_size is exceeded).

io.TextIOWrapper需要一个BufferedIOBase基类/接口，该基类/接口由io.StringIO和io.BytesIO提供，但不一定由TemporaryFile()返回的对象提供(尽管在我对OSX的测试中，TemporaryFile()返回了具有所需接口的_io.BufferedRandom对象，我的理论是这可能取决于平台).

io.TextIOWrapper requires a BufferedIOBase base class/interface, which is provided by io.StringIO and io.BytesIO, but not necessarily by the object returned by TemporaryFile() (though in my testing on OSX, TemporaryFile() returned an _io.BufferedRandom object, which had the desired interface, my theory is this may depend on platform).

因此，我希望您的MySpooledTempfile包装器在翻转后在某些平台上可能会失败.

So, I would expect your MySpooledTempfile wrapper to possibly fail on some platforms after rollover.

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