More Pythonic (or perhaps functional) way of creating this list?

Question

I'm returning a list of lists, but the following seems far more convoluted than it should be:

new_list = []
for key, value in group.items(): 
    new_list.extend([['%s%s%s%s%s' % (
    ncode, vendor, extra, value['suffix'], tariff),
    value['latest_cost'], value['rrp'], value['rb']] for tariff in value['trf']])
return new_list

Answer 1

That's not particularly convoluted. You have two "levels", the items in the group which you are expanding into one level. For doing that it's not very convoluted.

A more functional way would be to merge it all into one nested list expression, I think that could be possible. But it sure wouldn't be more readable, and personally I think that's unpythonic (ie, I don't like it).

Personally I would change that list expression to a for loop as well, for readability.

new_list = []
for key, value in group.items(): 
    for tariff in value['trf']:
        name = ''.join(ncode, vendor, extra, value['suffix'], tariff)
        new_list.append(name, value['latest_cost'], value['rrp'], value['rb']])
return new_list

Well, in fact, I would make a generator out of it, because I like them:

def tariffs(group):
    for key, value in group.items(): 
        for tariff in value['trf']:
            name = ''.join(ncode, vendor, extra, value['suffix'], tariff)
            yield [name, value['latest_cost'], value['rrp'], value['rb']]

You might also want to consider making objects out of this. As soon as you have lists of lists or dictionaries of dictionaries it's worth considering making classes instead.