Need to implement the Python itertools function "chain" in a class

Question

I am trying to emulate the "chain" function in itertools in python.

I came up with the following generator.

# Chain make an iterator that returns elements from the first iterable
# until it is exhausted, then proceeds to the next iterable, until all
# of the iterables are exhausted.
def chain_for(*a) :
    if a :
       for i in a :
          for j in i :
             yield j
    else :
       pass    

How can I emulate the same function in a class? Since the input to the function is an arbitrary number of lists, I am not sure if packing/unpacking can be used in classes, and if so I am not sure how to unpack in the 'init' method.

class chain_for :
   def __init__(self, ...) :
      ....
   def __iter__(self) :
      self
   def __next__(self) :
      .....

Thank you.

Answer 1

There is not (much) difference between def chain_for(*a): and def __init__(self, *a):. Hence, a very crude way to implement this can be:

class chain_for:
    def __init__(self, *lists):
        self.lists = iter(lists)
        self.c = iter(next(self.lists))

    def __iter__(self):
        while True:
            try:
                yield next(self.c)
            except StopIteration:
                try:
                    self.c = iter(next(self.lists))
                except StopIteration:
                    break
                yield next(self.c)

chain = chain_for([1, 2], [3], [4, 5, 6])
print(list(chain))

Outputs:

[1, 2, 3, 4, 5, 6]