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The C-API exposed by the `io` module on Python 3.1/3.2 is very limited, and makes interfacing with Python file objects in extension modules difficult.
In more detail:
1) Because the Python layer has buffering etc., the file handle returned by `PyObject_AsFileDescriptor` is not usable as-is. It requires flush and seek before use, every time there is a chance that the file object has been accessed on the Python side. 
2) There are no C-API functions such as the minimal set of `PyFile_Write(buf, length)`, `PyFile_Read(buf, length)`, `PyFile_Seek(pos, whence)`, `PyFile_Tell()`.
Instead, every call must go through PyObject_CallMethod, and the file objects only handle `PyBytes` and `PyByteArray` which are cumbersome and inefficient to use in extension modules.