From my understanding of the question, the lists are structured like [[1, 2, 3]].
This is an example of a two-dimensional list - albeit it a very useless one. If one consider another two dimensional list: [[1, 2], [3, 4]] The two lists inside the outer list can be treated as items of that list. ie:
a = [[1, 2],
[3, 4]]
a[0] --> [1, 2]
a[1] --> [3. 4]
So in your example, the simplest way to turn the 2 dimensional list into a one dimensional list is simply take the first element of the list (because the first element is actually the useful list).
a = [[1, 2, 3]]
b = [[4, 5, 6]]
plt.plot(a[0], b[0])
plt.plot([1, 2, 3], [4, 5, 6]) # is the same as above
plot(*x), though. You know the square brackets are the indication of a list right? You don't "get rid of" them anywhere.square bracketsare only information for you that you have list (or N-dimensional list) and not single value. You may need to use index - ie.some_list[0]