First, if your’re only interested in the first value, you should probably use a generator expression instead of a list comprehension, otherwise the loop will run for all mixed_widgets even though they won’t be used:

    (x for x in mixed_widgets if 'widgets' in x)[0]['widgets']

but this doesn't work, since you can’t do indexing [0] on a generator expression. No matter, next() returns the first value of any iterator:

    next(x for x in mixed_widgets if 'widgets' in x)['widgets']

Also, I think it the repetition of x in the 'x for x in' part is a bit ugly, we can fix that by moving the ['widgets'] attribute retrieval operation to inside the generator expression:

    next(x['widgets'] for x in mixed_widgets if 'widgets' in x)