a list > a list of lists

Question

In python, how can I split a long list into a list of lists wherever I come across '-'. For example, how can I convert:

['1', 'a', 'b','---', '2','c','d','---','3','123','e','---','4']

to

[['1', 'a', 'b'],['2','c','d'],['3','123','e'],['4']]

Many thanks in advance.

Answer 1

In [17]: import itertools
# putter around 22 times
In [39]: l=['1', 'a', 'b','---', '2','c','d','---','3','123','e','---','4']

In [40]: [list(g) for k,g in itertools.groupby(l,'---'.__ne__) if k]
Out[40]: [['1', 'a', 'b'], ['2', 'c', 'd'], ['3', '123', 'e'], ['4']]

Answer 2

import itertools

l = ['1', 'a', 'b','---', '2','c','d','---','3','123','e','---','4']
r = []

i = iter(l)
while True:
  a = [x for x in itertools.takewhile(lambda x: x != '---', i)]
  if not a:
    break
  r.append(a)
print r

# [['1', 'a', 'b'], ['2', 'c', 'd'], ['3', '123', 'e'], ['4']]

Answer 3

Here's one way to do it:

lst=['1', 'a', 'b','---', '2','c','d','---','3','123','e','---','4']
indices=[-1]+[i for i,x in enumerate(lst) if x=='---']+[len(lst)]
answer=[lst[indices[i-1]+1:indices[i]] for i in xrange(1,len(indices))]
print answer

Basically, this finds the locations of the string '---' in the list and then slices the list accordingly.