Python iter() Method

What is Python iter() Method?

The iter() is a Python built-in method that returns an iterator for the given object.

The syntax of the iter() method is:

iter(object, sentinel)

Python iter() Method Parameters

The iter() methods take two parameters as an argument:

• object - the name of the object whose iterator has to be returned.
• sentinel (optional) - A numeric value that is used to represent the end of the sequence.

Let’s check some examples of the python iter() method.

Example 1: How to use the iter() method in python?

cars = ['BMW','AUDI','FORD']

My_iter = iter(cars)

print(My_iter)

print(type(My_iter))

print(next(My_iter)) # BMW
print(next(My_iter)) # AUDI
print(next(My_iter)) # FORD

Output:

<list_iterator object at 0x7fddb59cb820>
<class 'list_iterator'>
BMW
AUDI
FORD

We can use the next() method to print the elements of iteration, and the iteration will remember the next count via the internal count variable. Once the iteration is complete, it raises a StopIteration exception, and the iteration count cannot be reassigned to 0.

We can also use __next__() method with ithe ter() method to print the iterator.

Example 2: Using __next__() method in python iter() method.

cars = ['BMW','AUDI','FORD']

My_iter = iter(cars)

print(My_iter.__next__()) # BMW
print(My_iter.__next__()) # AUDI
print(My_iter.__next__()) # FORD

The output will be as follows.

BMW
AUDI
FORD

Example 3: Using iter() with custom objects.

class PrintNumber:
    def __init__(self, max):
        self.max = max

    def __iter__(self):
        self.num = 0
        return self

    def __next__(self):
        if(self.num >= self.max):
            raise StopIteration
        self.num += 1
        return self.num

print_num = PrintNumber(3)

print_num_iter = iter(print_num)
print(next(print_num_iter))  # 1
print(next(print_num_iter))  # 2
print(next(print_num_iter))  # 3

# raises StopIteration
print(next(print_num_iter))

The output will be as follows.

1
2
3
Traceback (most recent call last):
  File "", line 23, in <module>
    print(next(print_num_iter))
  File "", line 11, in __next__
    raise StopIteration
StopIteration

Rules of iter()

• If the user-defined object doesn’t implement __iter__(), and __next__() or __getitem()__, the TypeError exception is raised.
• If the sentinel parameter is also provided, iter() returns an iterator until the sentinel character isn’t found.