I have a list of strings which contains a sublist os strings:

ids = [u'spotify:track:3ftnDaaL02tMeOZBunIwls', u'spotify:track:4CKjTXDDWIrS0cwSA9scgk', [u'spotify:track:6oRbm1KOqskLTFc1rvGi5F',
u'spotify:track:045sp2JToyTaaKyXkGejPy']]

I tried to flatten it with:

[item for item in ids for item in sublist]

and

chain = itertools.chain(ids)

but these solutions split the strings...

how do I flatten the original list into

[u'spotify:track:3ftnDaaL02tMeOZBunIwls', u'spotify:track:4CKjTXDDWIrS0cwSA9scgk', u'spotify:track:6oRbm1KOqskLTFc1rvGi5F',u'spotify:track:045sp2JToyTaaKyXkGejPy']

?

You could use a simple loop with an isinstance check.

out = []
for i in ids:if isinstance(i, list):out.extend(i)else:out.append(i)print(out)  

Output:

['spotify:track:3ftnDaaL02tMeOZBunIwls','spotify:track:4CKjTXDDWIrS0cwSA9scgk','spotify:track:6oRbm1KOqskLTFc1rvGi5F','spotify:track:045sp2JToyTaaKyXkGejPy'] 

You could also use itertools.chain, but with an extra layer of preprocessing:

from itertools import chainout = list(chain.from_iterable([i if isinstance(i, list) else [i] for i in ids]))
print(out)    

With the same output.