Raising a "null" exception in Python

Question

I am trying to write a function that does error checking in the following way.

def check_var_type(var, var_name, type):
    t = type(var)
    if t is type or t is list:
        return None
    else:
        return TypeError(
            f"Invalid {var_name} type '{t.__module__}.{t.__name__}', "
            f"'{float.__module__}.{float.__name__}' or "
            f"'{list.__module__}.{list.__name__}' expected.")


my_var = 1
raise check(my_var, 'my_var', float)

My expectation of Python's raise command was that if I pass None to it, it would simply ignore it and raise no exception. The response, however, was:

TypeError: exceptions must derive from BaseException

I then had a look at Python's built-in exception types to see if something like Nonthing , NoError , etc. exists. No luck though.

I can, of course raise the exception in the check_var_type function, but I don't want to, since this would add an extra line to the stack trace.

So, my (perhaps silly) question is: How can I use raise to not raise an exception? :-)

Thanks

Answer 1

If you don't want to raise an exception, don't call raise (whose sole job IS to raise an exception).

Perhaps what you really want is to call raise from inside check_var_type when you actually do want to raise an exception, and just use return when you don't.

An alternative might be to leave check_var_type as is, but wrap the call to it in an if that one raises the exception returned when an exception is returned.