NUMB3RS

In Season 5, Episode 23 of NUMB3RS, a supposed IP address appears on screen, 275.3.6.28, which isn’t actually a valid IPv4 (or IPv6) address.

An IPv4 address is a numeric identifier that a device (or, on TV, hacker) uses to communicate on the internet, akin to a postal address in the real world, typically formatted in dot-decimal notation as #.#.#.#. But each # should be a number between 0 and 255, inclusive. Suffice it to say 275 is not in that range! If only NUMB3RS had validated the address in that scene!

In a file called numb3rs.py, implement a function called validate that expects an IPv4 address as input as a str and then returns True or False, respectively, if that input is a valid IPv4 address or not.

Structure numb3rs.py as follows, wherein you’re welcome to modify main and/or implement other functions as you see fit, but you may not import any other libraries. You’re welcome, but not required, to use re and/or sys.

import re
import sys

def main():
    print(validate(input("IPv4 Address: ")))

def validate(ip):
    ...

...

if __name__ == "__main__":
    main()

Either before or after you implement validate in numb3rs.py, additionally implement, in a file called test_numb3rs.py, two or more functions that collectively test your implementation of validate thoroughly, each of whose names should begin with test_ so that you can execute your tests with:

pytest test_numb3rs.py

Hints

Recall that the re module comes with quite a few functions, per docs.python.org/3/library/re.html, including search.
Recall that regular expressions support quite a few special characters, per docs.python.org/3/library/re.html#regular-expression-syntax.
Because backslashes in regular expressions could be mistaken for escape sequences (like \n), best to use Python’s raw string notation for regular expression patterns, else pytest will warn with DeprecationWarning: invalid escape sequence. Just as format strings are prefixed with f, so are raw strings prefixed with r. For instance, instead of "harvard\.edu", use r"harvard\.edu".
Note that re.search, if passed a pattern with “capturing groups” (i.e., parentheses), returns a “match object,” per docs.python.org/3/library/re.html#match-objects, wherein matches are 1-indexed, which you can access individually with group, per docs.python.org/3/library/re.html#re.Match.group, or collectively with groups, per docs.python.org/3/library/re.html#re.Match.groups.

Demo

Before You Begin

Log into cs50.dev, click on your terminal window, and execute cd by itself. You should find that your terminal window’s prompt resembles the below:

Next execute

mkdir numb3rs

to make a folder called numb3rs in your codespace.

Then execute

cd numb3rs

to change directories into that folder. You should now see your terminal prompt as numb3rs/ $. You can now execute

code numb3rs.py

to make a file called numb3rs.py where you’ll write your program. Be sure to also execute

code test_numb3rs.py

to create a file called test_numb3rs.py where you’ll write tests for your program.

How to Test

How to Test `numb3rs.py`

Here’s how to test numb3rs.py manually:

Run your program with python numb3rs.py. Ensure your program prompts you for an IPv4 address. Type 127.0.0.1, followed by Enter. Your validate function should return True.
Run your program with python numb3rs.py. Type 255.255.255.255, followed by Enter. Your validate function should return True.
Run your program with python numb3rs.py. Type 512.512.512.512, followed by Enter. Your validate function should return False.
Run your program with python numb3rs.py. Type 1.2.3.1000, followed by Enter. Your validate function should return False.
Run your program with python numb3rs.py. Type 192.168.001.1, followed by Enter. Your validate function should return False.
Run your program with python numb3rs.py. Type cat, followed by Enter. Your validate function should return False.

While leading zeros in IP addresses are technically possible in some contexts, they are generally discouraged due to potential ambiguity. For this problem, treat them as invalid. If you’d like to learn more about IP address formatting standards, see RFC 3986, Section 7.4.

How to Test `test_numb3rs.py`

To test your tests, run pytest test_numb3rs.py. Try to use correct and incorrect versions of numb3rs.py to determine how well your tests spot errors:

Ensure you have a correct version of numb3rs.py. Run your tests by executing pytest test_numb3rs.py. pytest should show that all of your tests have passed.
Modify the validate function in the correct version of numb3rs.py. validate might, for example, only check whether the first byte of the IPv4 address is valid. Run your tests by executing pytest test_numb3rs.py. pytest should show that at least one of your tests has failed.
Again modify the correct version of numb3rs.py. validate might, for example, mistakenly return True when the user inputs an incorrect IPv4 format. Run your tests by executing pytest test_numb3rs.py. pytest should show that at least one of your tests has failed.

You can execute the below to check your code using check50, a program that CS50 will use to test your code when you submit. But be sure to test it yourself as well!

check50 cs50/problems/2022/python/numb3rs

Green smilies mean your program has passed a test! Red frownies will indicate your program output something unexpected. Visit the URL that check50 outputs to see the input check50 handed to your program, what output it expected, and what output your program actually gave.

How to Submit

In your terminal, execute the below to submit your work.

submit50 cs50/problems/2022/python/numb3rs