lets say I have one list ['A','B','C']
and the second [1,2]
I want to create a new list [(A,1), (A,2), (B,1)...]
Obviously it can be trivially done using a for loop like this:
a = ['A','B','C']
b = [1,2]
c = []
for x in a:
for y in b:
c.append((x,y))
c
[('A', 1), ('A', 2), ('B', 1), ('B', 2), ('C', 1), ('C', 2)]
but how can I do it using the [x for x in...] syntax ?
You need the Cartesian Product of the two lists:
>>> from itertools import product
>>> list(product(a, b))
[('A', 1), ('A', 2), ('B', 1), ('B', 2), ('C', 1), ('C', 2)]
Unlike an explicit list comprehension, this is trivially scalable to any number of input iterables. See here for details.
Take a look at itertools.product:
>>> from itertools import product
>>> a = [ 'A', 'B', 'C' ]
>>> b = [ 1, 2]
>>> [ x for x in product(a, b) ]
[('A', 1), ('A', 2), ('B', 1), ('B', 2), ('C', 1), ('C', 2)]
Using python lists:
[(i, j) for i in a for j in b]
Using a module:
from itertools import product
list(product(a, b))
[x for x in...] syntax has name and it called list comprehension, you can write your loops between [ and ] and put inner most before your loops.
[(x, y) for x in a for y in b]
In your case the list comprehensions version could be:
>>> [(x, y) for x in "ABC" for y in [1,2]]
[('A', 1), ('A', 2), ('B', 1), ('B', 2), ('C', 1), ('C', 2)]
Note that the order matters, that is for a fixed x='A' the possible values of y are iterated first.
