[ROOT] Re: Getting TDirectory entries with pyROOT

From: WLavrijsen@lbl.gov
Date: Wed Jun 30 2004 - 22:41:11 MEST


Topher,

>  How do I gracefully check for a null TObject pointer in pyroot?

Use a boolean predicate, or if you want to turn it into a boolean value, use
the 'not not' trick. That is, from your example:

>>> this = tdir.Get("h400")
>>> print not not this
1
>>> that = tdir.Get("h401")
>>> print not not that
0
>>> if that:
...   that.GetName()
...
>>>                                # <- nothing, as 'that' evaluates to False

The assertion will be removed. You are quite right that an exception would
be far more appropriate. But that'll be for a later release.

>  How can I get the name (and title) of an object in a file without reading
> the whole thing into memory?

Isn't that a general ROOT question? I'll have a look into it later, but I need
to warn you that I know next to nothing of using ROOT, so I may not find an
answer.

HTH,
  Wim
-- 
Wim.Lavrijsen@cern.ch   --   WLavrijsen@lbl.gov   --   www.lavrijsen.net

"Stop making excuses for your software."    --first step towards quality



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