Use Await In Lambda Function Using Python

Use Await In A Python Lambda Function

The await keyword is used to implement the awaitable task in Python. The different tasks require different periods for implementation. Implementation of some tasks is necessary, so we need to find a way to implement them immediately. All these problems can be solved using the await keyword in Python. A lambda function stands for a user-defined function without a name. This function will help you write a function and its components within a single line.

We can’t directly use a lambda function with the await keyword. There is no async lambda function in Python. We are not allowed to use the await keyword in the lambda function as an argument. If we use this, then we will get an error. But we need some method to implement this combination of lambda function and await keyword.

You can learn more about async/await in this article.

Method 1 is an alternative way to implement this logic. Method 2 explains why we can’t implement this code directly. Let’s get started by understanding some basics.

Basics of Await Keyword and Lambda Function

Await Keyword

The await keyword has different abilities that are implemented under the asyncio library. The Asyncio library carries out the process of executing two or three programs at the same time. This is interesting because we can save a lot of time through this process. There are different capabilities of the asyncio library, which provides high-level APIs to control the execution of different processes. It also controls the subprocess. As we all know, all tasks are scheduled in the queue. We can also manage this queue using the asyncio library.

The list of operations performed using the asyncio library is long. Let’s focus on the await keyword this time. I have implemented one example based on the asyncio library and await keyword. If you try this code at your end and face any error like this: ‘ cannot be called from a running event loop’ then you need to use 2-line code before your original code.

import nest_asyncio

This 2-line code will help you handle the error.

import asyncio

async def main():
    print("Action One")
    await asyncio.sleep(5)
    print("Action Two")
Await Function In Python
Await Function In Python

Lambda Function

In any programming language, functions are used in almost every code to solve problems. Different types of functions are available in the Python language, like a built-in function or a user-defined function. One more type is available, and that is the ‘lambda function’. The lambda function can be defined without a name. I have implemented the program of addition using the lambda function. The lambda function takes only one expression of addition. Then, print the values.

add = lambda x, y: x + y
print(add(2, 3))  

Instead of the addition function, you can put your expression and arguments. This will save time, and your work will be done in 1-line.

Lambda Function In Python
Lambda Function In Python

In this way, we implement the lambda function in Python.

How do I implement the Lambda Function with the Await Keyword?

We have seen the basics of the await keyword and lambda function. Now, can we combine both in one code? Yes.

We can combine both, but with some conditions. A lambda function is nothing but concise code, is anonymous, and can be defined in a single line. These features of the lambda function will help the program implement simple and easy asynchronous operations.

In the code of asynchronous functions, the lambda function will help to add some functionality with a single line of code. The execution becomes easy. When we try the lambda function and await keyword together, it will throw some errors.

Lambda Function with Await Keyword- Example 1

Let’s start with a basic example where we are going to use the lambda function. Then, we will use the await keyword to suspend the coroutine.

import asyncio

async_lambda_function = lambda x: asyncio.sleep(x)

async def main():
    print("Start main")
    await async_lambda_function(2)
    print("End main")

In this code, we need to import the asyncio module. Let’s see the results for a better understanding.

Lambda Function With Await Function
Lambda Function With Await Function- Example 1

In this way, we can implement the await function with the lambda function in Python.

Lambda Function with Await Keyword- Example 2

In this example, let’s try to implement both on the same line. This example is very important because it is possible to use the await keyword and lambda function in the same code. We have seen this type of implementation in example 1. Now, we are trying to implement both on the same line. This one will clear up the idea of using the await keyword and lambda function together in a single code.

example.sort(key=lambda x: await somefunction(x))

If we try to implement these lines, we will get ‘ ‘await’ outside the async function.’ That’s why we are trying the approach suggested in Example 1. This way, we can implement both the await keyword and the lambda function together.

Limitations of Using Await and Lambda Function

As we have seen in both examples, the lambda function and await keyword can be used together in a single code. This is possible if we pass the lambda function as an asynchronous function. If we try to use them all in one line, then it will throw an error. This is easy for handling async functions and increasing their functionality. If we see clearly, the code is a bit complex and will throw errors in big models. So, this is not generally used as a solution. Also, implementing one-line logic is possible in a lambda function, but what if we have the logic of two or three lines? This will create a very tricky situation to handle.

Advantages of Using Await With Lambda Function

Quick and easy operations are possible due to the use of the lambda function in the code. The lambda function will help you write one-line logic in asynchronous programming along with the await keyword. This will enhance the code’s conciseness. Another example of using both in a single code is parallelizing API calls. This becomes easy due to the lambda function and await keyword. To facilitate asynchronous processing on collections of items, combining lambda functions with map(), filter(), or similar functional programming constructs comes in handy.


In this article, I explained some basic things related to the await keyword and the lambda function. These are some common features of the Python language that help implement parallelizing concepts and asynchronous programming. Both have different features and ways of implementation. I have implemented both in a single code. Example 1 will give a brief idea about how to implement both in a single code. Example 2 will explain the restriction on using both on the same line. This type of implementation has some advantages and limitations, which I have tried to explain in detail with the help of this article.


You can read the official documentation for the asyncio module, Stack Overflow Query.