Not sure how to title this question. I've run into a few situations where I have a list of data, maybe annotated with some property, and I want to collect them into groups.

For example, maybe I have a file like this:

some event
reading: 25.4
reading: 23.4
reading: 25.1
different event
reading: 22.3
reading: 21.1
reading: 26.0
reading: 25.2
another event
reading: 25.5
reading: 25.1

and I want to group each set of readings, splitting them on a condition (in this case, an event happening) so that I end up with a structure like

[['some event',
  'reading: 25.4',
  'reading: 23.4',
  'reading: 25.1'],
 ['different event',
  'reading: 22.3',
  'reading: 21.1',
  'reading: 26.0',
  'reading: 25.2'],
 ['another event',
  'reading: 25.5',
  'reading: 25.1']]

In it's generic form, it is: Look for a condition, collect the data until that condition is true again, repeat

Right now, I'd do something like

events = []
current_event = []

for line in lines:
    if is_event(line):
        if current_event:
            events.append(current_event)
        current_event = [line]

    else:
        current_event.append(line)
else:
    if current_event:
        events.append(current_event)


def is_event(line):
    return 'event' in line

which produces what I want, but it's ugly and hard to understand. I'm fairly certain there has to be a better way

My guess is that it involves some itertools wizardry, but I'm new to itertools and can't quite wrap my head around all of it.

Thanks!

Update

I've actually gone with Steve Jessop's answer with a Grouper class. Here's what I'm doing:

class Grouper(object):
    def __init__(self, condition_function):
        self.count = 0
        self.condition_function = condition_function

    def __call__(self, line):
        if self.condition_function(line):
            self.count += 1
        return self.count

and then using it like

event_grouper = Grouper(is_event)
result_as_iterators = (x[1] for x in itertools.groupby(lines, event_grouper))

and then to turn it into a dictionary I do

event_dictionary = [{event: readings} for event, *readings in result_as_iterators]

which gives

[
 {'some event': ['reading: 25.4', 'reading: 23.4', 'reading: 25.1']},
 {'different event': ['reading: 22.3','reading: 21.1','reading: 26.0','reading: 25.2']},
 {'another event': ['reading: 25.5', 'reading: 25.1']}
]