I want to use n different variables, let's say var{0}, var{1}, var{2}, ..., var{n-1}
How can I do this ?
for var{0} in range(n)
for var{1} in [x for x in range(n) if x!=var{0}]:
for var{2} in [x for x in range(n) if (x!=var{0} and x!=var{1})]:
...
for var{n-1} in [x for x in range(n) if (x!=var{0} and x!=var{1} and ... and x!=var{n-2})]:
Thank you
It seems like this is just permutations of range(n)
:
from itertools import permutations
for var in permutations(range(n)):
# do something with var[0], var[1], ..., var[n-1]
print var
According to the documentation
Permutations are emitted in lexicographic sort order. So, if the input iterable is sorted, the permutation tuples will be produced in sorted order.
I think that means this will give you the same ordering as the approach in your example. For n=3
you get:
(0, 1, 2)
(0, 2, 1)
(1, 0, 2)
(1, 2, 0)
(2, 0, 1)
(2, 1, 0)
If you are interested in how this is being generated, the source for itertools.permutations
has the equivalent python code in its comments (the actual implementation is in C):
def permutations(iterable, r=None):
'permutations(range(3), 2) --> (0,1) (0,2) (1,0) (1,2) (2,0) (2,1)'
pool = tuple(iterable)
n = len(pool)
r = n if r is None else r
indices = range(n)
cycles = range(n-r+1, n+1)[::-1]
yield tuple(pool[i] for i in indices[:r])
while n:
for i in reversed(range(r)):
cycles[i] -= 1
if cycles[i] == 0:
indices[i:] = indices[i+1:] + indices[i:i+1]
cycles[i] = n - i
else:
j = cycles[i]
indices[i], indices[-j] = indices[-j], indices[i]
yield tuple(pool[i] for i in indices[:r])
break
else:
return
in Python you can do:
for i in range(n**n):
vars = [(int(i/(n**(n-j))))%n for j in range(1,n+1)]
where vars is the list of vars you want
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