fits.append() does not support documented fits.open() kwargs

According to the append() documentation, it supports the kwargs that are supported in the open() function: http://docs.astropy.org/en/stable/io/fits/api/files.html#astropy.io.fits.append

However, I tried to use the scale_back kwarg value, but got this error:

TypeError: writeto() got an unexpected keyword argument 'scale_back'

To reproduce:

import tempfile
import numpy as np
from astropy.io import fits


def github_issue():
    _, file_path = tempfile.mkstemp(prefix='test_file_', suffix='.fits')

    with open(file_path, 'ab+') as append_test_file_handle:
      fits.append(filename=append_test_file_handle, data=np.empty((4,4)), overwrite=False, output_verify='silentfix', checksum=False, scale_back=True)

github_issue()

[saimn]

Looking at this with fresh eyes, I think that there are several things to do, because the inner function that is used is not always the same:

• if the file does not exist, writeto is used, and kwargs are passed here. The only option that can be used here is output_verify. We can keep it like this and document this properly.

• if the file exists, and filename is a string, fits.open is used. Here we need to pass kwargs.

• if the file exists, and filename is a file object, there is no additional argument to pass. We could maybe check that kwargs is empty and raise a warning if it is not empty ?

[at88mph]

Hello. My test case above still fails with version 3.1 (hash: 743055cada122d6da8704ad28452806690679ef5). This issue is not holding me up anymore as I’ve worked around it for now, but the bug persists.

Thanks!