Question

>>> import itertools
>>> n = [1,2,3,4]
>>> combObj = itertools.combinations(n,3)
>>>
>>> combObj
<itertools.combinations object at 0x00000000028C91D8>
>>>
>>> list(combObj)
[(1, 2, 3), (1, 2, 4), (1, 3, 4), (2, 3, 4)]
>>>
>>> for i in list(combObj): #This prints nothing
...     print(i)
...

1. How can i iterate through combObj ?

2. How can i convert
   [(1, 2, 3), (1, 2, 4), (1, 3, 4), (2, 3, 4)]
   to
   [[1, 2, 3], [1, 2, 4], [1, 3, 4], [2, 3, 4]]

Answer 1

Once you iterate through the itertools.combinations object once, it’s been used up and you can’t iterate over it a second time.

If you need to reuse it, the proper way is to make it a list or tuple as you did. All you need to do is give it a name (assign it to a variable) so it sticks around.

combList = list(combObject) # Don't iterate over it before you do this!

If you want to iterate over it just once, you just don’t call list on it at all:

for i in combObj: # Don't call `list` on it before you do this!
    print(i)

Side note: The standard way to name object instances / normal variables would be comb_obj rather than combObj. See PEP-8 for more info.

To convert the inner tuples to lists, use a list comprehension and the list() built-in:

comb_list = [(1, 2, 3), (1, 2, 4), (1, 3, 4), (2, 3, 4)]
comb_list = [list(item) for item in comb_list]