Re: Iterator instances not independent

On 12/8/25 02:41, Sarfraaz Ahmed via Tutor wrote:

 > for x in seqA:
 >      if (seqB.hasNext()):
 >          bStr = str(next(itB))
 >      else:
 >          bStr = "done"
 >      print("A =", next(itA), "B =", bStr)

> Hello Fran,
> 
> My first guess is that the "for" loop is also doing a "next" on seqA (
> apart from the explicit next() in the print statement at the end of the
> loop )
Indeed, each time through the for loop consumes one item from the 
iterator seqA - that's what iteration does - and then you additionally 
consume another.

When you write a loop to iterate, you want to do something with the 
values the iterator gives you, so the usual form is in pseudo-code:

for var in iterator:
     do-something-with-var

You do nothing at all with 'x', so alternating values from seqA are just 
lost.

You've understood some of the iteration protocol, as you're defining 
__iter__ and __next__. But this is kind of the Hard Way, writing a 
generator function is a lot easier - the use of the "yield" statement 
makes it a generator, which suspends execution until the next attempt to 
consume from it, so the context is there and you don't have to store 
state variables in a class instance. And you don't have to provide a 
function to query if the generator has more values to offer, because it 
will automatically raise a StopExecption if it's out of values, which, 
when iterating over it, just means "okay, we're done".

So a simple-minded rewrite of your Sequence could be something like:

def Sequence(last=10):
     i = 0
     while i < last:
         yield i
         i += 1
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