Vanity Plates

CS50 license plate

In Massachusetts, home to Harvard University, it’s possible to request a vanity license plate for your car, with your choice of letters and numbers instead of random ones. Among the requirements, though, are:

“All vanity plates must start with at least two letters.”
“… vanity plates may contain a maximum of 6 characters (letters or numbers) and a minimum of 2 characters.”
“Numbers cannot be used in the middle of a plate; they must come at the end. For example, AAA222 would be an acceptable … vanity plate; AAA22A would not be acceptable. The first number used cannot be a ‘0’.”
“No periods, spaces, or punctuation marks are allowed.”

In plates.py, implement a program that prompts the user for a vanity plate and then output Valid if meets all of the requirements or Invalid if it does not. Assume that any letters in the user’s input will be uppercase. Structure your program per the below, wherein is_valid returns True if s meets all requirements and False if it does not. Assume that s will be a str. You’re welcome to implement additional functions for is_valid to call (e.g., one function per requirement).

def main():
    plate = input("Plate: ")
    if is_valid(plate):
        print("Valid")
    else:
        print("Invalid")


def is_valid(s):
    ...


main()

Hints

Recall that a str comes with quite a few methods, per docs.python.org/3/library/stdtypes.html#string-methods.
Much like a list, a str is a “sequence” (of characters), which means it can be “sliced” into shorter strings with syntax like s[i:j]. For instance, if s is "CS50", then s[0:2] would be "CS".

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 plates

to make a folder called plates in your codespace.

Then execute

cd plates

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

code plates.py

to make a file called plates.py where you’ll write your program.

How to Test

Here’s how to test your code manually:

Run your program with python plates.py. Type CS50 and press Enter. Your program should output:
```
Valid
```
Run your program with python plates.py. Type CS05 and press Enter. Your program should output:
```
Invalid
```
Run your program with python plates.py. Type CS50P and press Enter. Your program should output
```
Invalid
```
Run your program with python plates.py. Type PI3.14 and press Enter. Your program should output
```
Invalid
```
Run your program with python plates.py. Type H and press Enter. Your program should output
```
Invalid
```
Run your program with python plates.py. Type OUTATIME and press Enter. Your program should output
```
Invalid
```

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/plates

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/plates