.copy() doesn't work for backed files

[gtca]

Modalities backed inside a .h5mu file can't be copied to a new location as expected:

>>> mdata = mu.read("rna_atac.h5mu", backed=True)
>>> mdata['rna'].copy("rna.h5ad")
KeyError: "Unable to open object (object 'mod' doesn't exist)"

[ilia-kats]

Either there is a serious bug in AnnData, or I'm not understanding the semantics of copy. It seems that a copy operation of a backed AnnData also overwrites the backing file of the original object:

In [3]: test = ad.read_h5ad("/home/kats/rna.h5ad", backed=True)

In [4]: test2 = test.copy("/home/kats/rna2.h5ad")

In [5]: test2.filename                                                                                                                                                                                    
Out[5]: PosixPath('/home/kats/rna2.h5ad')

In [6]: test.filename                                                                                                                                                                                     
Out[6]: PosixPath('/home/kats/rna2.h5ad')

And this issue is ultimately a consequence of that.

[gtca]

I am struggling to provide any reasonable explanation to that behaviour, thanks for noticing! Let's see if that might be resolved upstream indeed then.

[ilia-kats]

This should work with current AnnData master, closing. Please reopen if there are any more issues with this.