How do I remove extra parsing characters in a list?

Question

I have the following lists of lists:

animals = [('dog', 'cat'), ('mouse', 'bird')]

I would like to reduce it to:

animals = ['dog', 'cat', 'mouse', 'bird']

is there a simpler way to have the result above than doing something like this:

animals = [('dog', 'cat'), ('mouse', 'bird')]

final = []
for a in animals:
    final.append(a[0])
    final.append(a[1])
print final

Answer 1

You can use itertools.chain.from_iterable:

>>> from itertools import chain
>>> list(chain.from_iterable(animals))
['dog', 'cat', 'mouse', 'bird']

Or a nested list comprehension:

>>> [anim for item in animals for anim in item]
['dog', 'cat', 'mouse', 'bird']

For tiny list use the list comprehension version, otherwise use itertools.chain.from_iterable.

>>> animals = [('dog', 'cat'), ('mouse', 'bird')]
>>> %timeit list(chain.from_iterable(animals))
100000 loops, best of 3: 2.31 us per loop
>>> %timeit [anim for item in animals for anim in item]
1000000 loops, best of 3: 1.13 us per loop

>>> animals = [('dog', 'cat'), ('mouse', 'bird')]*100
>>> %timeit list(chain.from_iterable(animals))
10000 loops, best of 3: 31.5 us per loop
>>> %timeit [anim for item in animals for anim in item]
10000 loops, best of 3: 73.7 us per loop

>>> animals = [('dog', 'cat'), ('mouse', 'bird')]*1000
>>> %timeit list(chain.from_iterable(animals))
1000 loops, best of 3: 296 us per loop
>>> %timeit [anim for item in animals for anim in item]
1000 loops, best of 3: 733 us per loop