Type name mismatch for streamer and a corresponding branch for std::pair

[plexoos]

There seems to be some inconsistency between the type name know to the streamer on file and the branch type when reading branches automatically created from std::pair members. I am reading a ROOT tree with a simple std::pair<Double_t, Double_t> member split into branches and get the following error:

...
File "uproot/uproot/tree.py", line 248, in _attachstreamer
KeyError: b'pair<Double_t,Double_t>'

However, a streamer for 'pair<double,double>' does exist and can be used to read the .first and .second subranches. I verified this by simply replacing 'Double_t' with 'double' in submembers[base]._fTypeName on line https://github.com/scikit-hep/uproot/blob/master/uproot/tree.py#L248 when encounter this branch.

Is this something that can be fixed by mapping ROOT types to their C equivalents? See https://root.cern.ch/doc/master/RtypesCore_8h_source.html#l00031

[jpivarski]

Man, that's tough: I just get the streamer name as a string, not an object that can be broken down into components like that. In fact, I wonder why the name is different in different streamers...

To do this properly, we'd have to parse the strings as C++ and canonicalize them. (Part of why ROOT I/O needs Cling.) Fortunately, we know they're only types, which cuts out most of the language: types are identifiers, *, <...>, and [].

On the other hand, as long as it's only identifiers that are being mapped, a regular expression that matches at identifier boundaries would be valid— it could never confuse MuDouble_trigger for Double_t, for instance. It should be done once, when the streamers are loaded; that would be less dangerous than doing it in tree.py.

I'll give it a shot and point you to a branch to test. If it works for your file (and passes all the other tests), I'll include it.

[jpivarski]

Try PR #176. That ought to take all strings like Double_t to double (and the full list from ROOT that you provided).

[plexoos]

Yes, I confirm that this fixed my issue. Thank you!

[jpivarski]

This will go into uproot 3.2.8 shortly.