Deep reference ..? | Intertools.product()

Asked Jan 22 '23 at 19:24

Active Jan 23 '23 at 20:23

Viewed 31 times

The following (pseudo) code should insert only one ZERO per pair

from itertools import product

In [321]: 
for p in  product([[1],[2]],[[4],[5]]):
     p[0].insert(0,0)
     print(p)
Out [321]  
([0, 1], [4])
([0, 0, 1], [5])
([0, 2], [4])
([0, 0, 2], [5])
    
In [322]: 
for p in  product([[1],[2]],[[4],[5]]):
    q = p[:]    
    q[0].insert(0,0)
    print(q)
Out [322]  
([0, 1], [4])
([0, 0, 1], [5])
([0, 2], [4])
([0, 0, 2], [5])

I know that the reason is that the product() method passes the item by reference, but ..... I cant change its behavior..

Any solution?

itertools.product(*iterables, repeat=1)

edited Jan 23 '23 at 20:23

semmyk-research

asked Jan 22 '23 at 19:24

sten

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2

Just a terminology note: although it is frequently mislabled as pass by reference, this behavior is not caused by pass by reference, because Python doesn't support that evaluation strategy. – juanpa.arrivillaga Jan 22 '23 at 19:27
In any case, you just need to use a deep copy instead of the shallow `q = p[:]` – juanpa.arrivillaga Jan 22 '23 at 19:27
1

In other words, `p[:]` makes s copy of the outer tupple, but does not copy the inner lists (`q[0] is p[0]`!). – zvone Jan 22 '23 at 19:34
1

Use `q = copy.deepcopy(p)` – Barmar Jan 22 '23 at 20:11
2

Rather than using `insert` at all, put the zero in the list *before* computing the product: `product([[0,1], [0,2]], [[4],[5]])`. – chepner Jan 22 '23 at 21:02

Deep reference ..? | Intertools.product()

0 Answers0