And `explicit is better than implicit` is idiomatic python, but the language uses the most implicit characters available on the average keyboard (` ` and ` `) to denote control flow.
In that sense control flow only exists as the relation between other things, so it makes sense for it to be denoted that way. If a line with no code on it is indented in the forest and nobody hears it, does the line execute?
I write my python interactively in a repl, and often end up with deeply nested list comprehensions as a result. I always need to break them up to have any chance of understanding it even a day later.
Also, not nesting things is very idiomatic Python ("Flat is better than nested" is part of the Zen).
So, people generally don't think of nested list comprehensions as idiomatic.