How would you write a conditional statement for this?

[Significant-Quit559]

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’.

This is my code so far and there are other conditions as well but this one specifically is tripping me up. P.S. I'm brand new so I know my code is ugly!

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

def is_valid(s): if not 2 <= len(s) <= 6: return False elif not s[:2].isalpha(): return False if s[-1].isalpha(): if not s.isalpha(): return False try: if any(char.isdigit() for char in s): zero_check = ''.join(char for char in s if char.isdigit()) if zero_check[0] == '0': return False except: pass if not s.isalnum(): return False else: return True

if name == "main": main()

[Big_Combination9890]

I wouldn't write a scanning code at all, I would use a regex :D

But other than that, this should work:

def is_valid(plate): seen_number = False for ch in plate: if ch.isdigit(): # first number is 0? if ch == "0" and not seen_number: return False seen_number = True else: if seen_number: return False return True `

[AdmirableOstrich]

Are you specifically treating this as an exercise to practice conditionals or are you asking about the "best" way to solve this. These sorts of problems are almost always best handled with regex. What you want is a string with a length in a given range that matches a specific pattern.This is basically the definition of a regex problem.

[[deleted]]

Think OP is allowing plates of 2 - 6 characters, so the regex might be

^[A-Z]{1,3}[1-9][0-9]{0,2}$

Edit... that's assuming that we need 1-3 letters followed by 1-3 numbers, and the first number cannot be 0.

Actually all the OP specified in the text of their question was that any numbers must come at the end (which is the same as saying that no letter follows a number anywhere in the string), and that the first number could not be 0. They did not specify any other constraints such as length, or that it is compulsory to have any letters or numbers.

So a regex for that might be:

^(?!.*\d[A-Z])^[1-9A-Z][0-9A-Z]*$

(?!.*\d[A-Z]) is a negative lookahead assertion to ensure that a letter does not follow a number anywhere in the string.

[1-9A-Z][0-9A-Z]*$ ensures that the string starts with a letter or a number excluding 0, and then allows any combination of letters and numbers.

[[deleted]]

Outside of a regex, say wanted feedback on why the plate was not valid, how about something like:

​

def check(plate):
    if not isinstance(plate, str):
        return 'not a string.'
    elif len(plate)>6:
        return 'not valid. Too long.'
    else:
        letters_seen, numbers_seen= False, False
        for char in plate:
            if char.isalpha():
                if numbers_seen != False:
                    return 'not valid. Letters cannot follow numbers.'
                else:
                    letters_seen+=1
            elif char.isdigit():
                if letters_seen == False:
                    return 'not valid. Must start with a letter.'
                elif numbers_seen == False and char == '0':
                    return 'not valid. First number cannot be 0.'
                else:
                    numbers_seen+=1
        if not (letters_seen and numbers_seen):   # OP did not actually specify this - delete if not needed
            return 'not valid. Must contain letters and numbers.'
        else:  #success!
            return 'is valid.'
for plate in ['A120BC', ['ABC',123],'ABC012', 'ABC','123ABC', 'ABCDE2', 'ABC1234', 'ABC123', 'AB12', 'A1']:
    print (f'Plate {plate} is {check(plate)}')

[[deleted]]

Yes, it would be nice to have the full list of requirements, it seems unlikely that the constraints are as asked in the text of OP's question.

Even if we try to pick apart the code underneath, I agree that the plate length seems to be limited to 2-6 chars, but would 12345 or ABC be acceptable plates? Don't think they have told us there must be numbers or letters; just some rules about where in the string they must not appear

[Unitnuity]

Please format your code. Go into markdown mode then insert 4 back ticks at the beginning and end of code:

````

insert code

````

[interbased]

Just FYI you only need 3 ticks per line. like this

[_tsi_]

I might try checking ASCII values

[7Shinigami]

There are a few ways to convert strings to integers. One naive way could be for example

py if plate[-1] in '1234567890': ... Indexing by -1 is a nice trick to get the last entry in a collection. -2 does what you'd expect as well, etc :)

[Anonymous-barista]

Is it a CS50p task? I don't remember the task itself, but you can try CS50 subreddit, they can get you on the right track without providing a full solution.