Programmer's guide to python

7.6 Iterables

>Iterables are objects that can be iterated using loops. An object having a special method __iter__() is considered to be an iterable. It can be iterated as many times as required.
>Examples of iterables include sequence types such as list, tuple, str, bytes and bytearray. Also non-sequence types such as dict, set and others such as file, range, enumerate objects.
>A custom class can implement __iter__() (a magic method which should return an iterator object) or __getitem__() (which is the magic method for enabling indexing) method to make its object iterable. They can also become subscriptable/indexable if implemented using the __getitem__() method. Examples of non-indexable are dictionaries or sets.
>Iterables can be used in for loops and in built-in functions like map(), zip(), filter() etc.
>Checking built-in iterables.

## Checking if 'list' is a iterable,
# we can check if it has a '__iter__()' method using 'dir()'
# or using 'hasattr()'
print(hasattr([1, 2, 3], "__iter__"))  # True
# checking for 'tuple'
print(hasattr((1, 2, 3), "__iter__"))  # True
# checking if 'set' have '__iter__' method
print(hasattr({1, 2, 3}, "__iter__"))  # True


## Iterables can be used in for loops
for a in (34, 32, 55, 34, 56):
  print(a)  # 34 32 55 34 56

>Create a custom class that has iterable functionality.

## Example: Create a simple iterable object that returns multiplier
# of 10 by index
class TenMultiplier:
  def __init__(self):
      self.max_range = 10

  # implement '__getitem__()' or '__iter__()' method to enable iteration.
  # by implementing '__getitem__()' our object is also indexable
  def __getitem__(self, index):
      if index > self.max_range:
          # 'StopIteration' is raised to break the iteration in loops
          raise StopIteration
      return index * 10


my_object = TenMultiplier()
# Indexing our object
print(my_object[2])  # 20

# Iterating our object
for a in my_object:
  print(a)  # 0 10 20 30...100