Adventures in Machine Learning

One-Liner Functions in Python: How to Make Your Code More Efficient and Readable

Creating One Line Functions in Python: Using Function Header and Body or Lambda Function

Have you ever heard the term one liner function in Python? This refers to a method of writing a function using either a function header and body or a lambda function in a single line of code.

It’s a concise way to write functions, but not always the most efficient when it comes to readability and control flow. In this article, well explore the pros and cons of creating one line functions in Python and the different approaches you can take.

Using Function Header and Body in One Line

Let’s first take a look at the syntax of a one liner function using a function header and body. Heres an example of a basic function written in a single line:


def function_name(x, y): return x + y


In this case, `function_name` is the functions name, and `x` and `y` are the parameters.

The `return` statement at the end of the line defines the output of the function. One of the advantages of one line functions is their simplicity.

This approach allows programmers to write functions quickly, particularly for small, simple tasks. It saves time, space, and minimizes mistakes due to code repetition.

Moreover, one line functions can be used as a more concise, readable, and modular alternative to map/filter/reduce combinations. Here’s an example:


def compress(a): return [a[i] for i in range(len(a)) if i == 0 or a[i] != a[i-1]]


This function takes in a list `a` and removes consecutive, duplicate elements.

The control flow, for loop, and if statement, are all included in a single line, making it a particularly efficient implementation of a function. However, one of the limitations of using function headers and bodies is that it can become unpythonic.

For example, you cannot include an if statement with an else clause in a single line since it requires two separate statements:


def myfunc(x): return x if not isinstance(x, str) else None


To some, this syntax can feel unusual and difficult to interpret. It may also be difficult to read when multiple operations are chained together.

Therefore, one should not overuse this approach or reduce a function’s readability at the cost of saving space.

Using a Lambda Function

Now let’s take a look at using a lambda function to create a one liner function. Lambda functions are anonymous functions that are defined without needing to be named or declared in memory.

The syntax is quite straightforward:


lambda arguments: expression


Here’s a basic example of a lambda function:


g = lambda x: x*2


In this case, `g` is a lambda function that takes one argument (x) and returns x*2. One of the advantages of using lambda functions is that they are more concise than function definitions.

They are usually used when you need a simple, one-time function for a limited purpose. One common use case is in map/filter/reduce operations, where you need to perform a simple calculation on each element of a list.

However, one of the limitations of lambda functions is that they can become quite confusing, especially for beginners. Lambda functions can only contain a single expression and cannot contain commands or statements.

Therefore, if you are trying to create a more complex function with branching or additional commands, lambda functions can become difficult to read and understand. Additionally, writing a lambda function with more complicated syntax, like multiple arguments and a for loop, is generally less coherent and harder to understand than a longer, more explicit function.


In conclusion, creating one line functions can be a useful tool in Python programming, but it is important to consider the limitations as well. On one hand, using one line functions with a function header and body can be efficient for simple tasks and more concise than lengthy map/filter/reduce operations.

However, this approach can quickly become unpythonic and difficult to read, particularly if you are using more complex syntax. On the other hand, using lambda functions is efficient and easy to use for simpler tasks, but it can quickly become confusing if you try to use them for more complex functions.

Overall, the importance of code clarity and readability cannot be overstated. While one line functions may save space and time, it is important to make sure they are still easy to understand, especially as your codebase grows and becomes more complex.

Simple code is usually the best. Always consider if your code is easy for others to read and understand when you’re writing it, and you’ll be more likely to write code that is maintainable, scalable, and reliable.

In conclusion, creating one line functions in Python can be a useful time-saving tool. While both function headers and bodies and lambda functions are capable of producing concise code, it’s vital to consider the limitations and the importance of readability and clarity.

It’s suggested not to focus too much on saving space and time at the cost of readability and coherence. The main takeaway is to prioritize code that is simple and easily understood, especially as codebases get more extensive.

Maintaining straightforward syntax and code clarity presents an essential aspect of robust program design.