# anext() function in Python

## Introduction

`anext()` is a new function that came in Python 3.10 version. It returns the next item from an [asynchronous iterator](https://docs.python.org/3/glossary.html#term-asynchronous-iterator) when awaited, or *default* if given and the iterator is exhausted. This is the async variant of the `next()` built-in and behaves similarly. We'll discuss `next()` in a later part.

The syntax of the `anext()` function looks like this:

```python
anext(async_iterator[, default])

```

where `async_iterator` is an [asynchronous iterator](https://docs.python.org/3/glossary.html#term-asynchronous-iterator). It takes an optional parameter, which is returned when the iterator is exhausted.

## Examples

If you remember in the part where we had discussed [`aiter()` function](https://blog.ashutoshkrris.in/aiter-function-in-python), we had seen an example. We'll use a similar example here too.

To create a real async comprehension, we will need to call another `async def` function. Let's see an example:

```python
import asyncio

async def numbers(num):
    for i in range(num):
        yield i
        await asyncio.sleep(0.5)

async def check_odd(num):
    it = aiter(numbers(num))
    while True:
        x = await anext(it)
        if x % 2 != 0:
            print(f"{x} is Odd!!")

if __name__ == " __main__":
    event_loop = asyncio.get_event_loop()
    try:
        event_loop.run_until_complete(check_odd(10))
    finally:
        event_loop.close()

```

When you run this code, you'll get this output:

```bash
1 is Odd!!
3 is Odd!!
5 is Odd!!
7 is Odd!!
9 is Odd!!
Traceback (most recent call last):
  File "C:\Users\ashut\Desktop\Test\Blog-Codes\Built-Ins\anext\main.py", line 30, in <module>
    event_loop.run_until_complete(check_odd(10))
  File "C:\Users\ashut\AppData\Local\Programs\Python\Python310\lib\asyncio\base_events.py", line 641, in run_until_complete
    return future.result()
  File "C:\Users\ashut\Desktop\Test\Blog-Codes\Built-Ins\anext\main.py", line 12, in check_odd
    x = await anext(it)
StopAsyncIteration

```

In the above code, the `numbers()` function is an [asynchronous generator](https://docs.python.org/3/glossary.html#term-asynchronous-generator) that is yielding values. Further, we have defined another async function `check_odd()` that uses the `aiter()` function to create an [asynchronous iterator](https://docs.python.org/3/glossary.html#term-asynchronous-iterator). Then `anext()` function is used to get the next value from this [asynchronous iterator](https://docs.python.org/3/glossary.html#term-asynchronous-iterator). But if you see the output we encounter an error once we reach the end of the list. We can remove this error if we use the optional parameter.

```python
import asyncio

async def numbers(num):
    for i in range(num):
        yield i
        await asyncio.sleep(0.5)

async def check_odd(num):
    it = aiter(numbers(num))
    while True:
        x = await anext(it, 'end')
        if x == 'end':
            break
        elif x % 2 != 0:
            print(f"{x} is Odd!!")

if __name__ == " __main__":
    event_loop = asyncio.get_event_loop()
    try:
        event_loop.run_until_complete(check_odd(10))
    finally:
        event_loop.close()

```

When you run this code, you'll get this output:

```bash
1 is Odd!!
3 is Odd!!
5 is Odd!!
7 is Odd!!
9 is Odd!!

```

In the above code, we have added another parameter **'end'** to the `anext()` function. Once it returns **'end'**, we break the loop and hence we don't encounter any error this time.

## Conclusion

This was a brief introduction to `anext()` in Python. You can find more examples [here](https://python.hotexamples.com/examples/alternator/-/anext/python-anext-function-examples.html).