[Tut] Python next()

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Python next()

The

Code:

next(iterator)

function is one of Python’s built-in functions—so, you can use it without importing any library. It returns the next value from the

Code:

iterator

you pass as a required first argument. An optional second argument

Code:

default

returns the passed default value in case the iterator doesn’t provide a next value.



Syntax:

Code:

next(iterator, <default>)

Arguments:

• iterator – the next element is retrieved from the
  Code:

  iterator
  
  
• default (optional) – return value if iterator is exhausted (it doesn’t have a next element)
  

Related Tutorials:

• Python Keywords Cheat Sheet
  
  
• Python Iterators
  
  
• Yield Keyword
  
  
• Python Lists
  

Example 1: No Default Value

The following example shows the

Code:

next()

function in action—without using a default value in case the iterator is empty.

Code:

users = ['Alice', 'Bob', 'Carl', 'David'] # convert the list to an iterator users_iterator = iter(users) x = next(users_iterator) print(x) # Output: 'Alice' x = next(users_iterator) print(x) # Output: 'Bob' x = next(users_iterator) print(x) # Output: 'Carl' x = next(users_iterator) print(x) # Output: 'David'

Each time you call

Code:

next(iterator)

, the iterator returns the next element in the iterator over the Python list

Code:

users

.

But what happens if you call the

Code:

next()

function once more on the now empty

Code:

users_iterator

object?

Code:

x = next(users_iterator) print(x) ''' Traceback (most recent call last): File "C:\Users\xcent\Desktop\Finxter\Blog\HowToConvertBooleanToStringPython\code.py", line 22, in <module> x = next(users_iterator) StopIteration '''

Python throws a

Code:

StopIteration

error.

Let’s learn how to fix this!

Example 2: With Default Value

Not providing Python a solution to the problem that the iterator may be empty is a common source of errors! You can fix the errors by passing the optional

Code:

default

argument:

Code:

x = next(users_iterator, 42) print(x) # 42

Now, you cannot crash the

Code:

next(...)

function anymore! Go ahead and try it…

Interactive Shell

The interactive code shell offers you a way to try your newly gained skill—understanding the

Code:

next()

function. Can you crash the script by changing the default value?

https://trinket.io/embed/python/dc149801a3

Exercise: Run the code in the interactive shell. Now, change the default value & run again!

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