>>> 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)
...
How can i iterate through combObj ?
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]]
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]
To convert to a list of lists, you can do:
[list(item) for item in combObj]
list(map(list, combObj))generators are good because they don't use much memory. If you're using it a lot and have memory then save it as a tuple instead of a generator.
Otherwise I often make a function to return the generator each time I want to use it:
>>> def get_combObj():
... return itertools.combinations(n,3)
...
>>> for i in get_combObj():
... print list(i)
...
[1, 2, 3]
[1, 2, 4]
[1, 3, 4]
[2, 3, 4]
(you can call get_combObj() as much as you want)
