marsx marsx - 1 month ago 9
Python Question

getting every possible combination in a list

suppose I had something like this:

L1=['cat', 'dog', 'fish', 'rabbit', 'horse', 'bird', 'frog', 'mouse'...]

for x in L1:
input1= open('file_%s'%(x), 'r')
file1= pickle.load(input1)
for x in L1:
input2= open('file_%s'%(x), 'r')
file2= pickle.load(input2)


and I wanted to get every combination of files without repeating combinations that have already been done (once cat_dog is done do not do dog_cat again). Is there a way I could do this? My real list is in alphabetical order, if that makes any difference.

Answer

you can also do it as a generator:

L1=['cat', 'dog', 'fish', 'rabbit', 'horse', 'bird', 'frog', 'mouse']
tuples = [(x,y) for x in L1 for y in L1 if x != y]
for entry in tuples:
    if (entry[1], entry[0]) in tuples:
        tuples.remove((entry[1],entry[0]))
for pair in tuples:
    input1= open('file_%s'%(pair[0]), 'r')
    file1= pickle.load(input1)
    input2= open('file_%s'%(pair[1]), 'r')
    file2= pickle.load(input2)

After the first loop, the contents of tuples is:

('cat', 'dog')
('cat', 'fish')
('cat', 'rabbit')
('cat', 'horse')
('cat', 'bird')
('cat', 'frog')
('cat', 'mouse')
('dog', 'fish')
('dog', 'rabbit')
('dog', 'horse')
('dog', 'bird')
('dog', 'frog')
('dog', 'mouse')
('fish', 'rabbit')
('fish', 'horse')
('fish', 'bird')
('fish', 'frog')
('fish', 'mouse')
('rabbit', 'horse')
('rabbit', 'bird')
('rabbit', 'frog')
('rabbit', 'mouse')
('horse', 'bird')
('horse', 'frog')
('horse', 'mouse')
('bird', 'frog')
('bird', 'mouse')
('frog', 'mouse')