Implement a Python function named "calculate_variance" that takes a list of numbers as input, and returns the variance of the list. Use the formula for population variance (sum of squared differences from the mean divided by the total number of items in the list) to calculate the variance. Make sure that the function handles cases where the list contains zero or one element, and returns an appropriate result (e.g. 0 for an empty list, or None for a list with a single element). The function should also handle cases where the input list contains non-numeric or non-integer values, and raise a ValueError with a descriptive message. Add comments to your code to explain the purpose of the function and any other important details. Use appropriate variable names and follow PEP-8 style guidelines for your code.
This prompt doesn't seem malicious.