Python 3 replacement for PyFile_AsFile

Question

The following code works in Python 2:

from ctypes import *

## Setup python file -> c 'FILE *' conversion :
class FILE(Structure):
    pass
FILE_P = POINTER(FILE)
PyFile_AsFile = pythonapi.PyFile_AsFile # problem here
PyFile_AsFile.argtypes = [py_object]
PyFile_AsFile.restype = FILE_P
fp = open(filename,'wb')
gd.gdImagePng(img, PyFile_AsFile(fp))

But in Python 3, there is no PyFile_AsFile in pythonapi.

The code is an except from testPixelOps.py.

Answer 1

I just needed a way to convert a file object to a ctypes FILE* so that I can pass it to GD.

You are out of luck. That was possible in Python 2.x, but is not possible in Python 3.x. The documentation explains why not:

These APIs are a minimal emulation of the Python 2 C API for built-in file objects, which used to rely on the buffered I/O (FILE*) support from the C standard library. In Python 3, files and streams use the new io module, which defines several layers over the low-level unbuffered I/O of the operating system.

If you want a FILE* you are going to have to make one yourself, using the C standard library directly.

Answer 2

I didn't find a real answer to the problem, but I found out that if you don't need to convert the Python file object to a FILE* (i.e., you don't need to "share" the opened file), you can just use ctypes to call fopen from libc and get the FILE* like that.