11 Checkpoint: Functional Programming

Purpose

Reinforce in your mind the concept that a function can be passed as an argument into another function.

Problem Statement

Phone numbers in the U.S. are often stored as ten digits and two dashes in this format: "ddd-ddd-dddd" where each d is a digit. The first three digits are called the area code. For example, for many years, 208 was the area code for all phone numbers in the state of Idaho and 801 and 435 were the two area codes for phone numbers in the state of Utah. Some people, when entering their phone number, will not enter the area code and assume that other people will know the correct area code.

Assignment

Write a program named add_area_code.py that reads phone numbers from a text file and adds the area code "208-" to all phone numbers that don’t have an area code.

Helpful Documentation

The Reading Files article explains how to setup VS Code so that your Python program can read from a text file.
The preparation content for lesson 9 explains how to read the contents of a text file into a list.
The preparation content for this lesson explains higher-order functions, nested functions, lambda functions, and how to call the map function.

Steps

Do the following:

Download these two files: phone_numbers.txt and add_area_code.py and save them in the same folder.
Open the phone_numbers.txt file in VS Code and examine the phone numbers. Notice that some of the phone numbers do not have an area code and contain only seven digits.
Open the add_area_code.py file in VS Code. Read the comments in the program and then add the following code:
1. At line 12, write a call to the Python map function and pass the add_area_code function and phone_numbers list as arguments to the map function.
2. At line 32, write code that checks if the length of a phone number is less than 12 and if the length is less than 12 then adds the area code "208-" at the beginning of the phone number.

Testing Procedure

Verify that your program works correctly by following each step in this testing procedure:

Download, examine, and run this Python file named test_add_area_code.py that contains pytest test functions. Verify that all the test functions pass. If they don’t pass, fix the mistakes in your add_area_code function until they pass.

Run your program, which should print the list of corrected phone numbers as shown below. Examine the corrected phone numbers printed by your program and verify that all of them have an area code.

> python add_area_code.py
['208-318-1623', '208-384-7712', '986-314-1378', '307-377-4921',
 '208-671-7536', '986-228-7414', '208-693-6706', '208-274-2098',
 '208-854-3221', '208-361-9817', '208-422-3492', '208-631-1374',
 '986-533-9667', '208-158-9497', '208-892-9830', '208-477-5323',
 '406-204-8756', '208-805-2538', '208-913-9942', '208-216-9589',
 '406-138-9226', '801-644-6761', '208-814-4444', '208-822-6738',
 '208-892-1093', '208-936-6389', '435-656-5821', '435-605-8294',
 '208-271-1868', '208-894-6391', '208-232-4118', '208-132-2121',
 '208-515-8227', '208-848-2334', '208-426-1557', '208-952-4330',
 '208-998-2171', '208-743-9219', '208-944-4381', '208-589-7767',
 '208-407-3555', '208-928-9293', '208-957-5808', '208-940-6629',
 '208-825-9259', '208-123-7580', '208-374-8128', '208-847-4807',
 '986-159-8293', '208-515-9963', '406-241-6676', '208-907-1851',
 '208-297-6367', '208-936-8173', '208-376-7010', '208-681-1558',
 '208-800-4436', '208-590-8866', '208-788-1866', '208-163-7631',
 '208-928-8793', '406-595-2898', '208-330-3155', '208-884-7294',
 '208-120-4949', '801-343-8776', '208-362-3779', '208-482-2107',
 '208-366-5618', '435-957-8250', '208-441-5628', '307-494-6001',
 '208-571-5297', '208-366-7389', '801-730-8010', '208-134-6240',
 '208-402-3658', '208-151-9828', '208-485-7973', '208-506-2683',
 '208-518-9635', '208-769-7551', '208-776-1574', '208-604-4304',
 '208-119-9734', '208-917-6174', '208-773-1167', '307-749-5991',
 '208-334-8971', '208-995-8602', '208-193-5073', '208-345-4015',
 '208-367-8633', '208-289-6515', '208-265-8998', '208-800-3565',
 '208-211-2706', '208-408-3950', '208-928-3119', '208-691-9409']

Ponder

In the main function, look at the line of code that calls the map function. Think about the fact that the map function will call the add_area_code function once for each element in the phone_numbers list, and the add_area_code function will add the area code "208-" at the beginning of each phone number if necessary.

Sample Solution

When your program is finished, view the sample solution for this assignment to compare your solution to that one. Before looking at the sample solution, you should work to complete this checkpoint program. However, if you have worked on it for at least an hour and are still having problems, feel free to use the sample solution to help you finish your program.

Submission

When complete, report your progress in the associated I‑Learn quiz.