Misleading IOError when passing a urlopen object in to fits.open()

Per this SO question: http://stackoverflow.com/questions/32643206/how-do-i-open-a-fits-file-from-a-url-in-astropy

As noted in the answers, one can already pass a URL as a string in to fits.open() and that will work fine. A urlopen object has never been supported (intentionally) in the first place. But it could be supported easily so long as the file is opened in readonly (or denywrite) mode. It just needs to be handled explicitly. In any case the error message one gets is also misleading:

ERROR: IOError: File-like object does not have a 'write' method, required for mode 'ostream'. [astropy.io.fits.file]

This happens despite not explicitly requesting 'ostream' mode.

Do you mean a Request object?

So something like:

>>> import urrlib.request
>>> from astropy.io import fits
>>> obj = urllib.request.Request("http://google.com")
>>> type(obj)
<class 'urllib.request.Request'>
>>> fits.open(obj)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/sanket/astropy/astropy/io/fits/hdu/hdulist.py", line 138, in fitsopen
    return HDUList.fromfile(name, mode, memmap, save_backup, cache, **kwargs)
  File "/home/sanket/astropy/astropy/io/fits/hdu/hdulist.py", line 280, in fromfile
    save_backup=save_backup, cache=cache, **kwargs)
  File "/home/sanket/astropy/astropy/io/fits/hdu/hdulist.py", line 801, in _readfrom
    ffo = _File(fileobj, mode=mode, memmap=memmap, cache=cache)
  File "/home/sanket/astropy/astropy/io/fits/file.py", line 143, in __init__
    self._open_filelike(fileobj, mode, clobber)
  File "/home/sanket/astropy/astropy/io/fits/file.py", line 455, in _open_filelike
    % self.mode)
OSError: File-like object does not have a 'write' method, required for mode 'ostream'.

@SanketDG

@SanketDG Probably, though this needs to work on Python 2 as well, so also whatever's returned by urllib2.urlopen which I think is something else.

Really anything with a read() method but no write() method.

@embray

@embray would it be better to explicitly check for the urlopen object in fitsopen()
or in _File()?

All the actual I/O details are handled in the _File class. fitsopen is purely a UI.

@embray

@embray is this issue solved if not can i work on this issue

@AMAN3003

@AMAN3003 On GitHub, issues / pull requests that are related to each other show up as cross-references when one references the other. For example, just above your comment you should be able to see two pull requests that reference this issue. One of this PRs is already merged, and references this issue in passing. The other, you can see, is already an attempt to work on this issue (which still needs some work, but it's getting there).

Relatedly, we need to do better at setting the "assignee" to an issue that someone is working on. I think part of this is a UI problem though--GitHub doesn't allow setting an assignee to someone who isn't watching the project.

It appears that this actually already works as expected, at least for the latest version of astropy:

import urllib.request
from astropy.io import fits

with urllib.request.urlopen('file:///path/to/file/that/exists.fits') as urlobj:
    with fits.open(urlobj) as fits_handle:
        # go to town ...

I added a new unit test demonstrating as much in PR #6378, so hopefully this resolves the issue.

Nothing quite feels so good as a bug that resolved itself. 😂

@pllim

@pllim - I'm sure there are still a few hiding in the crowd of the 664 open issues that are solved themselves 😉

Navigation Menu

Repository navigation

Misleading IOError when passing a urlopen object in to fits.open() #4165

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Misleading IOError when passing a urlopen object in to fits.open() #4165

Description

Activity

SanketDG commented on Sep 20, 2015

embray commented on Sep 21, 2015

lingxz commented on Oct 14, 2015

embray commented on Oct 15, 2015

AMAN3003 commented on Jan 25, 2016

embray commented on Jan 25, 2016

drdavella commented on Jul 19, 2017

pllim commented on Jul 19, 2017

bsipocz commented on Jul 20, 2017

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions