classname_of gives Exception when used on TBranch

[jrueb]

Please consider the following source code

import uproot
import numpy as np


with uproot.recreate("test.root") as f:
    f["Tree"] = {"x": np.array([1,2,3,4,5])}

f = uproot.open("test.root")
print(f.classname_of("Tree/x"))

I would expect it to print "TBranch". However, it actually raises an exception: AttributeError: 'Model_TTree_v20' object has no attribute 'key'.

Uproot version: 4.1.9

[jpivarski]

I hadn't thought of this as a potential use, but since "/" hides the distinction between paths into nested directories and paths into nested branches, it makes sense that one would try passing such a path into classname_of, streamer_of, class_of, title_of, etc.

The difficulty is that the path-handling is a specialized implementation in uproot.ReadOnlyDirectory.key

https://github.com/scikit-hep/uproot4/blob/3fe33aff6d6ed88203eed90f4edb5f2bc720f3e6/src/uproot/reading.py#L2006-L2021

which would have to get generalized out to be able to use them in the other functions that take paths.

Or maybe it just means that uproot.TBranch.HasBranches objects (i.e. TTree and all TBranch classes) should have a key method? (What about TBranches that contain TBranches? Would that work? I'm talking to myself...) Such a method can't return an uproot.reading.ReadOnlyKey because TTrees and TBranches don't have them the way that uproot.ReadOnlyDirectory does, but maybe a mocked "FakeKey" could duck-type to supply the appropriate information...

[jpivarski]

This feature request is still open, but I'm not going to attempt to get it in before the 5.0.0 release (next Monday). I'm just removing that label.