python - More simplified explanation of chain.from_iterable and chain() of itertools

Question

Can you give a more simplified explanation of these two methods chain() and chain.from_iterable from itertools?

I have searched the knowledge base and as well the python documentation but i got confused.

I am new to python that's why I am asking a more simplified explanation regarding these.

Thanks!

Answer 1

You can chain sequences to make a single sequence:

>>> from itertools import chain

>>> a = [1, 2, 3]
>>> b = ['a', 'b', 'c']
>>> list(chain(a, b))
[1, 2, 3, 'a', 'b', 'c']

If a and b are in another sequence, instead of having to unpack them and pass them to chain you can pass the whole sequence to from_iterable:

>>> c = [a, b]
>>> list(chain.from_iterable(c))
[1, 2, 3, 'a', 'b', 'c']

It creates a sequence by iterating over the sub-sequences of your main sequence. This is sometimes called flattening a list. If you want to flatten lists of lists of lists, you'll have to code that yourself. There are plenty of questions and answers about that on Stack Overflow.