Adding Lists Elements to 'Mega List'

Question

Let's say I have a list somewhere called majorPowers which contain these two lists:

axis=["germany","italy","japan"]
allies=["russia","uk","us"]

I'd like to insert each of the elements of these lists, into a new mega-list. I'm currently doing this:

>>> temp = []
>>> temp = [ww2.append(t) for t in majorPowers]
>>>ww2
[['germany','italy','japan'],['russia','uk','us']]

How do I adjust this to not use the temp and to insert the individual elements into ww2 instead of the lists themselves(axis and allied).

Also, would the new mega-list itself be classed as a comprehensive list, or the process of making it?

EDIT:

Please note I do not want to do:

for a in list1:
    for b in a:
        c.append(b)

@S.Lott. I understand your point. However I'm trying to learn some of the tricks in Python, instead of the standard way I'd usually do things. This is just to open my mind to Python a little more!

Answer 1

from itertools import chain
ww2 = list(chain.from_iterable(majorPower))

Answer 2

It is good that you ask this question, because it is bad form to misuse list comprehensions like that. The code you show uses append, not to generate the elements of temp, but because of its side effects. Avoid side effects in list comprehensions!

So, there are a couple of things you can do. First, you can use itertools.chain:

>>> from itertools import chain
>>> list(chain(*mayorPowers))
['germany', 'italy', 'japan', 'russia', 'uk', 'us']

Instead of passing the elements of mayorPowers as individual arguments to chain, you can also use itertools.chain.from_iterable:

>>> list(chain.from_iterable(mayorPowers))
['germany', 'italy', 'japan', 'russia', 'uk', 'us']

Or you can use extend:

>>> ww2 = []
>>> for mp in mayorPowers:
...     ww2.extend(mp)
...
>>> ww2
['germany', 'italy', 'japan', 'russia', 'uk', 'us']

Or sum (I like this one most, I suppose):

>>> sum(mayorPowers, [])
['germany', 'italy', 'japan', 'russia', 'uk', 'us']

Or, to be a little crazy (uses functools.reduce and operator.add),

>>> from functools import reduce
>>> from operator import add
>>> reduce(add, mayorPowers)
['germany', 'italy', 'japan', 'russia', 'uk', 'us']

Answer 3

try extend

for t in majorPowers: ww2.extend(t)

or

sum(majorPowers,[])

Answer 4

I would use reduce:

from operator import add
ww2 = reduce(add, majorPowers)