Incorrect length causing int not iterable error

0
votes

I am attempting to loop through a matrix, called lattice, randomly using the randrange function. My matrix is an 8x8 and prints fine. However when I attempt to randomly loop through each element of this matrix I am getting the error

'TypeError: 'int' object is not iterable'

Due the upper limit of the range, len(mymatrix). I'm unsure as to why this is. 

   for R1 in randrange(0, (len(lattice)):
        for R2 in randrange(0, len(lattice)):
            H = -j*lattice[R1,R2]*(lattice[R1+1,R2],lattice[R1-1,R2], lattice[R1,R2+1],lattice[R1,R2-1]) +h*lattice[R1,R2]
            H_flip = -j*-1*mymatrix[R1,R2]*(lattice[R1+1,R2],lattice[R1-1,R2], lattice[R1,R2+1],lattice[R1,R2-1]) +h*lattice[R1,R2]
    print lattice[R1,R2]

I have not used randrange in a loop before, is it perhaps that it can't be used the same way range is used? I've also tried to set the range as: 

for R1 in randrange(0, len(lattice)-1)

I thought maybe the length was one too long but to no avail.

2
pythonpython-2.7matrix
Please post the some more details of your code as well as the the full error. - Vasilis G.
Just read the docs what random.randrange returns and compare it to what range returns. - Michael Butscher
Why are you trying to loop randomly? - Olivier Melançon

2 Answers

0
votes

You are correct. randrange() returns a single element from within the given range. On the other hand, range() returns a list of elements, and is therefore iterable.

You could try something like this:

stop = randrange(0, len(lattice)-1)
start = randrange(0, stop)
for R1 in randrange(start, stop):
     for...
0
votes

The method randrange does not return a range, but a randomly selected element instead as can be read in the doc.

random.randrange(start, stop[, step])

Return a randomly selected element from range(start, stop, step). This is equivalent to choice(range(start, stop, step)), but doesn’t actually build a range object.

That is why you get a TypeError, you are indeed trying to loop over an int.

I would not recommend looping in a random order over your lists, but if it turns out to be necessary, I would use shuffle.

from random import shuffle

# shuffle mutates your list so we need to do the following
rows, cols = range(len(lattice)), range(len(lattice))
shuffle(rows)
shuffle(cols)

for R1 in rows:
        for R2 in cols:
            # ...

Note that in Python3, you would need to cast your range to a list first.