Importing necessary type hints

from typing import List

Defining a function named 'calculate_sum' which accepts a list of integers as input and returns an integer as output

def calculate_sum(lst: List[int]) -> int:

# Initializing a variable named 'result' with a value of 0
result = 0

# Iterating through each element in the input list 'lst'
for num in lst:
    
    # Checking if the current element is greater than 0
    if num > 0:
        
        # If the current element is greater than 0, add it to the 'result' variable
        result += num

# Returning the final result obtained after iterating through the entire input list
return result

The above code defines a function 'calculate_sum' which calculates the sum of all positive integers in a given list. The function accepts a list of integers as input and returns the sum of all positive integers in the input list as output.