values/errors read

[archiron]

Hi, I started to work with uproot and I have a weird effect;
if after opening a root file and reading an histo [1], I try to read the _values/_errors arrays [2], I only empty arrays returned.

If before reading I use a statement such as :
values_1 = hist_1_4.values()
errors_1 = hist_1_4.errors()
then, I can have access to the _values/_errors arrays as in point [2].
Is this way correct and known ?

Arnaud

[1] : fileName1 = rootFilesPath + '/' + "DQM_V0001_R000000001__RelValZEE_14__CMSSW_12_1_0_pre2-121X_mcRun3_2021_realistic_v1-v1__DQMIO.root"
histoPath = "DQMData/Run 1/EgammaV/Run summary/ElectronMcSignalValidator"
datasets = ['h_ele_PhiMnPhiTrueVsEta_pfx']
rootFile = up4.open(fileName1)
root_tree_1_4 = rootFile[histoPath]
hist_1_4 = root_tree_1_4[dataset]

[2] : for n1, v1 in hist_1_4.dict.items():
if n1.startswith("_values"):
allValues_1 = v1
elif n1.startswith("_errors"):
allErrors_1 = v1

[jpivarski]

I don't remember what's in _values and _errors, but they're probably caches.

A general rule in Python is that anything that starts with an underscore is an internal detail, equivalent to private in C++, not part of the library's interface. Private functions/classes/attributes/variables won't, in general, behave in predictable ways, and they can be removed or changed from one version of a library to the next.

So the important question is whether values() and errors() behave as you expect. These methods don't start with underscores and they're documented (here: values and errors, and also as satisfying a general protocol (UHI), which gives the same meaning to these methods across multiple libraries). Thus, they're part of the public interface.

Also, it would help if code snippets in GitHub are surrounded by triple-backticks, since this formats them as code. Particularly in Python, the meaning of the code depends on indentation, and without the formatting, the indentation is removed!

[archiron]

Hi, thanks for your reply.
I actually wanted to use _values / _errors because It does not contains under/overflow values. But in fact, this is easier to use official form such as values() or errors().

Arnaud

P.S.
sorry for the code format I forgot to use.