Rob - 11 months ago 57

Python Question

So i wanted to make a function that takes positive integer

`n`

`n-tuples`

`True/False (1/0)`

`f(1) = (0,),(1,)`

f(2) = (0, 0), (0, 1), (1, 0), (1, 1)

My code was:

`def fill(n: int) -> Tuple[Tuple[int]]:`

if n == 1:

return (0,),(1,)

return tuple((i + j) for i in fill(n-1) for j in fill(1))

I've heard python isn't very good with recursion, and generally feel this isn't effective solution.

It seemed like using powerset of a range of a given number (recipe for powerset is from the

`itertools`

`from itertools import chain, combinations`

def range_powerset(n: int):

s = list(range(n))

return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))

def indicator(A: Iterable, B: Iterable):

return tuple(i in A for i in B)

def fill2(n: int):

return (indicator(i, range(n)) for i in range_powerset(n))

Yet it seems like too much work for a pretty basic thing.

Is there a better way to do it?

Answer

What you describe is not a powerset but a Descartes product with repetition. Use `itertools.product`

:

```
import itertools
def fill(n):
return itertools.product((0,1), repeat=n)
print(list(fill(3)))
# [(0, 0, 0), (0, 0, 1), (0, 1, 0), (0, 1, 1), (1, 0, 0), (1, 0, 1), (1, 1, 0), (1, 1, 1)]
```

Source (Stackoverflow)