python函数参数引发什么异常

Question

I'm creating a function right now that takes in two lists. I want these two lists to be of equal size. I'm trying to figure out what kind of exception I should throw (or If I should throw an exception at all) if they aren't the same size. I kind of want to say ValueError but this is a check that doesn't actually pertain to any single value.

For clarities sake, here's my function stub.

def create_form(field_types, field_discriptions):
    pass

Answer 1

You can create your own subclass of exception called ArraysNotEqualSizeException. Might be a bit overkill, but it gets the point across.

Answer 2

I would just use assert and raise an AssertionError :

assert len(field_types) == len(field_descriptions), "Helpful message"

Otherwise, ValueError with a message seems like the best choice.

Answer 3

throw an exception as the first thing in the function. A function-critical error should not do anything without making sure it can do what it wants or it could have bad effects

This isn't a giant error; you should use an assert

Places to consider putting assertions:

checking parameter types, classes, or values checking data structure invariants checking "can't happen" situations (duplicates in a list, contradictory state variables.) after calling a function, to make sure that its return is reasonable - Python wiki

assert len(listone) == len(listtwo), 
    "the function cannot continue because\
     the two arguments passed are of invalid length"

a ValueError as suggested by Blender would be the right type if you want to use a generic exception, however that's usually reserved for larger issues and would be less helpful.

for quick reference:

"ValueError

Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value, and the situation is not described by a more precise exception such as IndexError." - Python docs