Use strings for colors in Python tutorials

[guitargeek]

This makes the code less verbose and more pythonic.

Sister PR in roottest:
root-project/roottest#1227

[linev]

I would provide return value for all Set...Color methods with color index.
One could check then if method really changed something.

[guitargeek]

I know, that would be nice, but the existing versions of the Set*Color( methods are virtual, so we can't change their return types without causing incompatibilities :(
For example:
https://github.com/root-project/root/blob/master/core/base/inc/TAttLine.h#L40

[pcanal]

What is the typical Python behavior if the name is incorrect spelt? I.e. should the new SetLineColor (and co) print an error message?

[guitargeek]

Right now, it will just silently do nothing. Not sure yet if this should be treated as an Error: also when you call the old SetLineColor() with an invalid integer, it doesn't complain, and when drawing it falls back to black.

[pcanal]

For reference, an arbitrary example of what is done by a python library:

>>> color_name_to_rgba("unknown")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/igraph/drawing/colors.py", line 517, in color_name_to_rgba
    components = palette.get(int(color))
                 ^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'get'

So I guess the answer to my original question is likely 'throw' an exception that is caught by the interpreter.

also when you call the old SetLineColor() with an invalid integer,

The difference is that with: SetColor(some_arbitrary_number), I might expect to have to check the return value, since there is no reason to expect that all numbers are valid. With SetColor(ROOT.kBlue), I am guaranteed that it just works (if it misspelt there will be am interpretation error). With SetColor("Bleue"), I confident I got it right, humm or did I spelt in French :).

More concretely, if the goal is to be "more pythonic." we should also seriously consider applying the python recommendation on how to handle those kind of error cases.

[guitargeek]

You are right, the cases are not comparable. Would raising a std::invalid_argument be okay for you?

It would look like this:

Traceback (most recent call last):
  File "/home/rembserj/spaces/master/root/src/root/test.py", line 5, in <module>
    h.SetLineColor("kReed")
cppyy.gbl.std.invalid_argument: void TAttLine::SetLineColor(const string& lcolor) =>
    invalid_argument: "kReed" is not a valid color name

[pcanal]

Sounds fair.

[github-actions]

Test Results

    18 files      18 suites   3d 23h 29m 0s ⏱️
 2 678 tests  2 678 ✅ 0 💤 0 ❌
46 490 runs  46 490 ✅ 0 💤 0 ❌

Results for commit 8ff4f78.

♻️ This comment has been updated with latest results.

[pcanal]

LGTM but we need to rebase ...

[guitargeek]

Thanks for the ping @pcanal! Is it okay now? Could you approve together with the roottest PR?

By the way there was recently a forum discussion about color names in Python, which tells us again that this is a feature that our users will appreciate:
https://root-forum.cern.ch/t/color-names-in-python/62543/3