Unable to execute an example in official site , doctest_mark_exe is not defined

I just installed graphviz, but I could not even execute the first operation.

doctest_mark_exe()

From the example here where I tried to make a simple graph.

I have attached a screen shot: I wonder what am I missing?

The README of GitHub - xflr6/graphviz: Simple Python interface for Graphviz appears to be wrong. I don’t see how the doctest_mark_exe step could work as nothing prior to this defines or imports that symbol. You might want to report the issue there.

There are few things as frustrating as trying to learn a new (fill in the blank) and right off the bat, the instructions don’t work (or do work, but I messed them up and can’t find my mistake). I commiserate.

If your goal is to learn both Python and Graphviz, my suggestion would be to learn them one-at-a-time. Or at least get dangerous with one before tackling the other.
If one is more important to you than the other, I suggest starting with the more important language.

I’d also note that that the web page you referenced may be someone’s official page, but it is not a Graphviz official page.

Good luck, and feel free to ask more Graphviz questions.