Appending to a list comprehension in Python returns None

This is a question out of curiosity rather than trying to use it for a practical purpose.

Consider I have the following simple example where I generate a list through list comprehension:

>>> a = [1, 2, 3]
>>> b = [2 * i for i in a]
>>> b
[2, 4, 6]
>>> b.append(a)
>>> b
[2, 4, 6, [1, 2, 3]]

However if I try and do this all in one action

>>> a = [1, 2, 3]
>>> b = [2 * i for i in a].append(a)
>>> b == None
True

The result returns None. Is there any reason why this is the case?

I would have thought that an action like this would either return an answer like in the first example or throw an error.

For reference I'm using Python 3.6.5

append only works on variables, not list literals, since it updates the list object itself and does not return the resulting list.

As @Tomalak mentioned noted, running a similar operation on a simple list also returns None

>>> [1, 2, 3].append(4) == None
True

You can use concatination + instead of append in list comprehension

In [1]: a = [1, 2, 3]

In [2]: b = [2 * i for i in a] + [a]

In [3]: b
Out[3]: [2, 4, 6, [1, 2, 3]]