iter()

The iter() function returns an iterator object.

iter(object, sentinel[optional])

The object is required and must either be a collection (e.g., a list) or callable (e.g., a class with a __call__() method).

If the object is callable, the optional sentinel parameter can be applied and the iterable will end when the returned value is the same as the sentinel and a StopIteration error will be raised.

The example below demonstrates how the iter() function is used in a Python program:

cars = ['Ferrari', 'Lamborghini', 'Porsche']

cars_iter = iter(cars)

print(next(cars_iter))
print(next(cars_iter))
print(next(cars_iter))

This will print the following output:

Hello, World! Let's count:
2
3
4
5
6
7
8
9
StopIteration Exception raised. Value returned was equal to sentinel value

The following example applies the optional sentinel parameter through a callable class object (though the __call__() method):

class codeNinjaCount:
  def __init__(self, greeting, num):
    self.greeting = greeting
    self.num = num
    print(f"{self.greeting}! Let's count:")

  def __call__(self):
    self.num += 1
    return self.num

codeNinjaIterable = iter(codeNinjaCount("Hello, World", 1), 10)

while True:
  try:
    print(next(codeNinjaIterable))
  except StopIteration:
    print("StopIteration Exception raised. Value returned was equal to sentinel value")
    break

Codebyte Example

When using iterables, it usually isn’t necessary to call iter() or deal with iterator objects. The for loop does this automatically by creating a temporary, unnamed variable to hold the iterator for the duration of the loop.

The following code examples use the iter() function and a for loop to produce the same results:

Code
Output
Loading...
Run