Which of the following errors indicates an operation was attempted on a non-existent index or key?

• A. KeyError
• B. ValueError
• C. IndexError
• D. TypeError

Answer: (A)

The answer is keyError, as this error occurs when a dictionary operation attempts to access a key that does not exist within that dictionary. In Python, dictionaries are collections of key-value pairs, and each key must be valid and present for the operation to succeed. If you try to retrieve a value using a key that isn't defined in the dictionary, Python raises a KeyError. This is a precise indication that the operation can't be fulfilled because the key is not available.

While IndexError might seem relevant, it specifically relates to list or tuple operations where an attempt is made to access an index that is out of the range of the existing indices. ValueError can arise in various situations where a function receives an argument of the right type but an inappropriate value, and TypeError occurs when an operation is performed on a data type that is not suitable for that operation. None of these specifically denote the scenario concerning a missing key in a dictionary, which makes KeyError the correct and relevant choice in this context.