In Python, a lambda function is a small, anonymous function that can be created without a name. They are often called “lambda functions” or “anonymous functions” and are useful for creating small, throwaway functions for specific tasks. They are defined using the lambda keyword, followed by a list of arguments and a single expression. The expression is evaluated and returned when the lambda function is called.

Here’s an example of a simple lambda function that takes two arguments and returns their sum:

sum = lambda x, y: x + y
result = sum(3, 4)
print(result) # Output: 7

Lambda functions are often used in conjunction with other built-in functions such as filter, map, and reduce. These functions take a function as an argument, which is then applied to each element in a list or other sequence. Here’s an example of using a lambda function with the filter function:

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
even_numbers = filter(lambda x: x % 2 == 0, numbers)
print(list(even_numbers)) # Output: [2, 4, 6, 8, 10]

This example uses the lambda function to filter out odd numbers from the list by checking if the number is divisible by 2.

Another example is using map function, which applies a given function to all items in an input_list.

numbers = [1, 2, 3, 4, 5]
squared_numbers = map(lambda x: x**2, numbers)
print(list(squared_numbers)) # Output: [1, 4, 9, 16, 25]

Lambda functions are useful when you need a small, throwaway function for a specific task and don’t want to clutter your code with a named function. They are also useful when you need to pass a function as an argument to another function, such as in the examples I provided with filter and map. Another example could be sorting a list of tuples by the second element of the tuple, you can use the lambda function as the key argument in the sorted function.

tuples = [(1, 'c'), (2, 'b'), (3, 'a')]
sorted_tuples = sorted(tuples, key=lambda x: x[1])
print(sorted_tuples) # Output: [(3, 'a'), (2, 'b'), (1, 'c')]

Lambda functions are not as powerful as regular functions, but they can be used in situations where regular functions would be overkill. They can also make your code more concise and readable. Keep in mind that lambda functions are limited to a single expression and can’t contain statements or annotations. If you need more complex logic or error handling, it’s best to use a regular function.