# Converting a list of lists to a single list

Terry Reedy tjreedy at udel.edu
Wed Jul 24 01:02:44 CEST 2013

```On 7/23/2013 5:52 PM, steve at divillo.com wrote:
> I think that itertools may be able to do what I want but I have not
> been able to figure out how.

A recursive generator suffices.

> I want to convert an arbitrary number of lists with an arbitrary
> number of elements in each list into a single list as follows.
>
> Say I have three lists:
>
> [[A0,A1,A2], [B0,B1,B2] [C0,C1,C2]]
>
> I would like to convert those to a single list that looks like this:
>
> [A0,B0,C0,C1,C2,B1,C0,C1,C2,B2,C0,C1,C2,
>  A1,B0,C0,C1,C2,B1,C0,C1,C2,B2,C0,C1,C2,
>  A2,B0,C0,C1,C2,B1,C0,C1,C2,B2,C0,C1,C2]

def crossflat(lofl):
if lofl:
first = lofl.pop(0)
for o in first:
yield o
yield from crossflat(lofl.copy())

A0, A1, A2 = 100, 101, 102
B0, B1, B2 = 10, 11, 12
C0, C1, C2 = 0, 1, 2
LL = [[A0, A1, A2], [B0, B1, B2], [C0, C1, C2]]
cfLL = list(crossflat(LL))
print(cfLL)
assert cfLL == [
A0, B0, C0, C1, C2, B1, C0, C1, C2, B2, C0, C1, C2,
A1, B0, C0, C1, C2, B1, C0, C1, C2, B2, C0, C1, C2,
A2, B0, C0, C1, C2, B1, C0, C1, C2, B2, C0, C1, C2]

passes

--
Terry Jan Reedy

```