In this assignment, you are going to write a Python program to demonstrate the IPO (Input-Process-Output) cycle that is the heart of many imperative programs used for processing large amount of data. Daisy is recently hired by a warehouse. One of her job is to keep track the items ordered by all the branches of the company. The company wants to automate the task using a computer program. Being a friend of Daisy, she knows you are a Computer Science major; so she recommended outsourcing the contract for writing the computer program to you. However, the timeline is short; and you only have less than three weeks to finish the job. The following is a description on the requirements: General requirements: o The program you write must be a Python 3.x program, it cannot be written in any other language, not even in Python 2.x. You have to provide source code, and the company will run your program on a standard Python 3 implementation. Your program should produce no errors and/or warnings during execution. o Your program will be a console program. There is no need to produce a window-based graphical user interface. o Your program will have a main function named main. It takes two parameters. The first one being the name of the input data file, and the second is the name of the output result file; both are strings. You can assume that both the input and output files can be open without any problem. Therefore, there is no need to check for the result of opening the files. Input requirements: o The input data file is guaranteed to contain only numbers and plus or minus sign, as well as the space and newline characters. o The first line has only one (1) number, representing the number of items the system should manage. This number is guaranteed to be less than or equal to ten thousand (10,000). o Each of the subsequence line is a transaction line which contains exactly two (2) numbers, separated by space characters. The first is an integer representing the item number (the items are numbered from 1 onward); and the second is an integer representing the quantity ordered by the branches. The two numbers are separated by one or more of space characters.

o The number of transaction lines is not known in advance but guaranteed to be less than or equal to 1 billion (1,000,000,000). Output requirements: o For each order line read, you need to echo the line to the output, using the format '%5d %10d'. o If the order data is not valid, you need to output the reason why it is not valid on the same line of the echo output, using the format '%5d %10d %s'. All invalid orders must be echoed but ignored in the processing. o The following explain the error conditions (in the following, n represents the number of items involved, and in the example outputs represents a space character): If the item number is not between 1 and n, inclusively, the item is invalid: 141878invaliditemnumber If the quantity is not a positive value, it is invalid: 61-610invalidquantity If a line has multiple errors, only one error needed to be reported. The following shows the priority of errors, from high to low: Invalid item. Invalid quantity. The following example shows the echoed line in case of multiple errors: -12-922invaliditemnumber o After you have echoed all order lines, you should output the number of valid orders in a separate line. There should be a blank line before and after this line. The format should be '%10d'. o After that, you need to output a summary for all items, if and only if there are any orders for the item. The format, again, should be '%5d %10d'. o All lines in the output file should have no trailing space or tab characters

Additional information and requirement: 1. Your program should contain at least three (3) top-level functions (including the main function). You probably will end up having more than 3 functions. 2. You cannot have any import statement in your program. 3. You cannot have any global variables 4. You cannot have any class definition in your program (this assignment is NOT about object-oriented programming). 5. You cannot have anything other than top-level function definitions in your program (not even a call to the main function the tester will call it). 6. Since you only know the number of items when you run the program, you will need some sort of lists or matrices with dynamic storage to hold data. 7. Since there can be potentially up to 1 billion transactions in the input data file. You cannot read them all into a list and process them later (doing so may cause an out-of-memory error), you must process them as you read them in. 8. Your program must be a Python 3.x program. 9. You can assume that the input file contains no format error