How to split a list on a condition?

Question

By now I didn't find a convenient way to split a list by certain conditions, for example, I have a record list:

 a = ((0,1),(1,0),(0,2),(1,0),(3,0),(4,0),(0,3),(1,5)....)

I want to split the content into 2 lists

alist = []
blist = []
for x in a:
    if x[0] == 0:
        alist.append(x)
    elif x[0] == 1:
        blist.append(x)

Not very concise.

Written as list comprehensions:

aList = [x for x in a if x[0] == 0]
bList = [x for x in a if x[0] == 1]

List comprehensions are usually good for reading and performance, but in this case the list must be iterated twice.

Is there a better way to do this job?

Answer 1

Adding one line will make the loop more concise at the cost of readability (and FPness).

alist = []
blist = []
bothlists = [alist, blist]
for x in a:
  bothlists[x[0]].append(x)