Appending a list's elements to another list using a list comprehension

[Debajit Adhikary]

I have two lists:

a = [1, 2, 3]
b = [4, 5, 6]

What I'd like to do is append all of the elements of b at the end of
a, so that a looks like:

a = [1, 2, 3, 4, 5, 6]

I can do this using

map(a.append, b)

How do I do this using a list comprehension?

(In general, is using a list comprehension preferable (or more
"pythonic") as opposed to using map / filter etc.?)