How can I cleanly combine a number of prefixes of the same string?

Question

For example, if my string is

lst= [44,44 , 44]

and my prefix lengths are

lens = [2, 2, 2]


   for k,v in zip(key,value):
         #dic[k] = v
         dic[k].append(v)

I made this with defaultdict

od = collections.OrderedDict(sorted(dic.items(),reverse=True))
od-> OrderedDict([('44', [2,2,2])])

I want to iterate through the [2,2,2] and make a string equivalent to

'44'[:2] + '44'[:2] + '44'[:2] 

and end up with a single string like '444444' .

Answer 1

For your original example (which seems a bit over-complicated):

import collections

x = collections.OrderedDict([('4444', [1, 1, 1, 1, 2])])
print(''.join([k[:v] for k, vs in x.items() for v in vs]))

Explanation:

• ''.join(<some list here>) takes a list and joins its elements into a string separated by the given string.
• [k[:v] for k, vs in x.items() for v in vs] is a list comprehension, taking every key k and values vs (which is a list in your case) from the items of a dictionary, and then taking every value v from that list and adding k[:v] for each combination to the list in order.

In general, if you have a list and a string and you'd like to create a concatenation of prefixes of that string based on the lengths in the list:

s = '12345'
ls = [1, 1, 2, 1, 3]
result = ''.join([s[:l] for l in ls])

Not sure what good it would be though...