Iterator for variable number of nested loops

I'm trying to write an iterator for something like this (simplified from original problem):

import numpy as np

class IterableNumber:
  def __init__(self, digits):
    self.digits = digits
    self.zero_indices = np.where(digits == 0)[0]
  def __iter__(self):
    return self
  def next(self):
    # For each index in self.zero_indices, loop 1 through 9?
    pass
  # Other methods omitted

The IterableNumber takes an array of numbers, but '0' is a wild card. When I loop through this object, I want each '0' digit to loop through a range of 1 through 9, i.e.

num = IterableNumber(np.array([5, 5, 0, 5, 0]))
for digits in num:
  print digits

should print

[5, 5, 1, 5, 1]
[5, 5, 1, 5, 2]
...
[5, 5, 1, 5, 9]
[5, 5, 2, 5, 1]
[5, 5, 2, 5, 2]
...
...
[5, 5, 9, 5, 9]

Writing this iterator for the general case seems to require recursion in order to take care of the variable number of nested loops (one for each 0 present), as other threads on this site would suggest. But how do I write such a recursive function in the context of the iterator's next() function? Or maybe there's another way to solve this problem altogether? Any insight would be appreciated :)

I'm on python 2.7.3 if it's relevant.