Iteration protocol

generators.py

# --- iterators ---
# Если у объекта есть методы __iter__() __next__() значит он является итератором

class MyIter(object):
    
    def __init__(self, start, stop):
        self._current = start
        self._stop  = stop
      
    def __iter__(self):
        return self
      
    def __next__(self):
        if self._current < self._stop:
            result = self._current
            self._current += 1
            return self._current
        raise StopIteration
        
q = MyIter(0, 5)
qq = iter(q)
next(qq)
# -------------------------------------------------
class ExampleIterator:
    def __init__(self, data):
        self.index = 0
        self.data = data
        
    def __iter__(self):
        return self

    def __next__(self):
        if self.index >= len(self.data):
            raise StopIteration

        result = self.data[self.index]
        self.index += 1
        return result

class ExampleIterable:
    def __init__(self, data):
        self.data = data

    def __iter__(self):
        return ExampleIterator(self.data)

[i**2 for i in ExampleIterable([1,2,3])]
[1, 4, 9]

#  F O R   vs   W H I L E
product = 1
for i in [1,2,3,4]:
    product *= i
print(product)

product = 1
i = iter([1,2,3,4])
while True:
    try:
        product *= next(i)
    except StopIteration:
        break
print(product)