Python: Linking Lists Together

Question

Suppose I have a list where each index is either a name, or a list of rooms the preceding name index reserved.

[["Bob"],["125A, "154B", "643A"],["142C", "192B"], ["653G"], 
["Carol"], ["95H", 123C"], ["David"], ["120G"]]

So in this case, Bob has the rooms: 125A, 154B, 643A, 152C, 192B, and 653G reserved, etc.

How do I construct a function which would make the above into the following format:

[["Bob", "125A, "154B", "643A", "142C", "192B", "653G"], ["Carol"... 

Essentially concatenating [name] with all the [list of room reservations], until the next instance of [name]. I have a function which takes a list, and returns True if a list is a name, and False if it is a list of room reservations, so effectively I have:

[True, False, False, False, True, False, True False] for the above list, but not sure how that would help me, if at all. Assume that if a list contains names, it only has one name.

Answer 1

Given the following method

def is_name(x):
  return # if x is a name or not

a simply and short solution is to use a defaultdict

---

Example:

from collections import defaultdict

def do_it(source):
  dd = defaultdict(lambda: [])
  for item in sum(source, []): # just use your favourite flattening method here
    if is_name(item):
      name = item
    else:
      dd[name].append(item)
  return [[k]+v for k,v in dd.items()]

for s in do_it(l):
  print s

---

Output:

['Bob', '125A', '154B', '643A', '142C', '192B', '653G']
['Carol', '95H', '123C']
['David', '120G']

---

Bonus:

This one uses a generator for laziness

import itertools 

def do_it(source):
  name, items = None, []
  for item in itertools.chain.from_iterable(source):
    if is_name(item):
      if name: 
        yield [name] + items
        name, items = None, []
      name = item
    else:
      items.append(item)
  yield [name] + items