<think>
Okay, let's see. I need to implement the code_valid function. The function checks if a code is valid based on two conditions: the length of the code must exactly match the given length, and the code can only contain uppercase letters and digits. Also, the length has to be greater than zero, otherwise, it's invalid.

First, I need to make sure that the length is greater than zero. If the length is zero or less, I should raise a ValueError. Wait, the problem says to reject a stated length of zero or less with an error. So, the function should first check if the length is less than or equal to zero. If so, raise a ValueError with a message like "Length must be greater than zero".

Next, check the length of the input code. If the length of the code is not equal to the given length, return False. So, len(code) != length.

Then, check each character in the code. Each character must be either an uppercase letter (A-Z) or a digit (0-9). So, for each character in code, check if it is in the allowed set. How to do that? Maybe using a loop or a generator expression.

So, for each char in code, check if it is a digit or uppercase letter. How to check that? Well, in Python, we can check if a character is a digit using char.isdigit(), and if it's uppercase using char.isupper(). But wait, the code is a string, so each character is a single character. So, for each character in code, we need to verify that it is either a digit or an uppercase letter.

So, the steps are:

1. Check if length is <= 0. If yes, raise ValueError.
2. Check if the length of code is equal to the given length. If not, return False.
3. Check each character in code to ensure it is a digit or uppercase letter. If any character is invalid, return False.
4. If all checks pass, return True.

Now, implement this in Python.

Wait, the function is called code_valid, and it takes code (a string) and length (int) and returns a bool.

So, code_valid function:

def code_valid(code: str, length: int) -> bool:
    if length <= 0:
        raise ValueError("Length must be greater than zero")
    if len(code) != length:
        return False
    for c in code:
        if not (c.isdigit() or c.isupper()):
            return False
    return True

Wait, but what about the case where the code is empty? For example, if length is 5, but code is an empty string. Then len(code) is 0, which is not equal to 5, so it returns False. That's correct.

Also, if the code is "A1", length 2: valid. If code is "A1b", length 3: invalid because 'b' is not uppercase or digit.

But wait, the problem says that the code must hold nothing but capital letters and digits. So, the code can't have lowercase letters, spaces, or other characters.

So the check is correct: each character must be a digit or uppercase letter.

But wait, what about the case where the code is "A1", length 2: that's valid. What if the code is "A1B", length 3: valid.

But what if the code is "A1 2" (with a space)? Well, the problem says that the code may not have spaces. Wait, the user mentioned that the code may not have spaces between groups. Wait, the original problem says: "Whether a code may hold