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.