Stochastic simulation event timing
If you're writing a simulation, it's probably worthwhile to add some abstractions to your code so that you can free your mind to think at a more abstract level.  Ideally, I would like to see

L = list(until_total(stop_time, poisson_process(10)))


(Consider not calling list() if you just need an iterable and not a list.)

Here is one way to get there:

from itertools import takewhile
from random import expovariate

def poisson_process(rate):
    while True:
        yield expovariate(rate)

def until_total(limit, iterable):
    total = [0]                 # http://stackoverflow.com/q/2009402
    def under_total(i):
        total[0] += i
        return total[0] &lt; limit
    return takewhile(under_total, iterable)

stop_time = next(poisson_process(1))
L = until_total(stop_time, poisson_process(10))


Also, consider using more meaningful identifiers:

customer_arrivals = poisson_process(10)
cashier_yawns = poisson_process(1)
customer_interarrival_times = until_total(next(cashier_yawns), customer_arrivals)