In Python, a lambda function is an anonymous function defined using the lambda keyword. To find the sum of elements in a list using a lambda function, one typically combines it with the reduce function from the functools module. The reduce function applies the lambda function cumulatively to the items of the list, reducing the list to a single value.
Here is a step-by-step guide on how to accomplish this:
Step 1: Import the reduce Function
The reduce function needs to be imported from the functools module.
from functools import reduce
Step 2: Define the Lambda Function
The lambda function will take two parameters and return their sum. In this case, it adds together two elements.
sum_function = lambda x, y: x + y
Step 3: Create a List of Elements
Prepare the list of numbers you wish to sum.
numbers = [1, 2, 3, 4, 5]
Step 4: Apply the reduce Function
Use the reduce function along with the lambda function to calculate the sum of the elements in the list.
total_sum = reduce(sum_function, numbers)
Step 5: Output the Result
Finally, print the result to see the total sum.
print(total_sum) # Output: 15
Complete Example
Putting it all together, the complete code looks like this:
from functools import reduce
# Define the lambda function for summation
sum_function = lambda x, y: x + y
# List of numbers to sum
numbers = [1, 2, 3, 4, 5]
# Calculate the sum using reduce and the lambda function
total_sum = reduce(sum_function, numbers)
# Output the result
print(total_sum) # Output: 15
Alternative Method: Using sum()
While using reduce with a lambda function is a valid approach, Python provides a built-in sum() function that accomplishes the same task more succinctly:
total_sum = sum(numbers)
print(total_sum) # Output: 15
Using sum() is generally preferred for its simplicity and readability. However, understanding the use of lambda functions with reduce is beneficial for scenarios requiring custom aggregation beyond simple summation.