how to inquire an iterator in python without changing its pre-inquire state

Question

I built an iterable object A that holds a list of other objects B. I want to be able to automatically skip a particular object B on the list if it is flagged bad when the object A is used in a for loop.

class A():
  def __init__(self):
    self.Blist = [B(1), B(2), B(3)] #where B(2).is_bad() is True, while the other .is_bad() are False

  def __iter__(self):
    nextB = iter(self.Blist)
    #if nextB.next().is_bad():
    #   return after skip
    #else:
    #   return nextB

However, I cannot figure out how to write the conditional that is commented in pseudo code above, without skipping the iteration inquired (the else clause fails)

Thanks!

Answer 1

You can use a generator function:

  def __iter__(self):
      for item in self.Blist:
          if not item.is_bad():
              yield item

A generator function is marked by the keyword yield. A generator function returns a generator object, which is an iterator. It will suspend execution at the yield statement and then resume processing when the calling routine calls next on the interator.