random iteration in Python

Question

When you want to iterate sequentially over a list of numbers you will write:

for i in range(1000):
  # do something with i

But what if you want to iterate over the list of numbers from the range (0..999) randomly? There is a need (in every iteration) to choose randomly the number that wasn't chosen in any previous iteration and there is a need to iterate over all of the numbers from the range (0..999).

Do you know how to do that (smart)?

Answer 1

You can use random.shuffle() to, well, shuffle a list:

import random

r = list(range(1000))
random.shuffle(r)
for i in r:
  # do something with i

By the way, in many cases where you'd use a for loop over a range of integers in other programming languages, you can directly describe the "thing" you want to iterate in Python.
For example, if you want to use the values of i to access elements of a list, you should better shuffle the list directly:

lst = [1970, 1991, 2012]
random.shuffle(lst)
for x in lst:
  print x

NOTE: You should bear the following warning in mind when using random.shuffle() (taken from the docs:

Note that for even rather small len(x), the total number of permutations of x is larger than the period of most random number generators; this implies that most permutations of a long sequence can never be generated.