StopIteration Exception in Python

To understand StopIteration Exception, you need to understand how iterators work in Python.

1. Iterator is an object that holds values which can be iterated upon.
2. It uses the __next__() method to move to the next value in the iterator.
3. When the __next__() method tries to move to the next value, but there are no new values, a StopIteration Exception is raised.

Example 1

Code

y = [1, 2, 3]
x = iter(y)
print(x.__next__())
print(x.__next__())
print(x.__next__())
print(x.__next__())

Output

1
2
3
Traceback (most recent call last):
  File "some_file_location", line 6, in <module>
    print(x.__next__())
StopIteration

You can catch such errors using the StopIteration Exception class.

Example 2

Code

y = [1, 2, 3]
x = iter(y)
try:
    print(x.__next__())
    print(x.__next__())
    print(x.__next__())
    print(x.__next__())
except StopIteration as e:
    print("StopIteration error handled successfully")

Output

1
2
3
StopIteration error handled successfully

Check out other Python Built-in Exception classes in Python.

built-in-exception-classes - Pylenin

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