Q:

python: is there an isError function?

is there a function that will return true if some_function returns an error?

A:

No. Python uses exceptions to handle errors, and these are caught using try...catch blocks.
In other words, what is your definition of an error? False? Null? ""?
Edit:
To answer your question in the comment, there is no well-defined way of comparing, say, "1.1" and "1.2". This is intentional, because there is no obvious ordering on strings. Now in fact, Python does support comparing strings, but it uses lexicographic (alphabetical) ordering, which isn't what you want. This is because these strings are semantically floats -- they represent numbers. Now the real problem is that they shouldn't have been strings in the first place (because they're numbers!), but sometimes you can't fix that. So instead, turn them into numbers:
float(1.1) > float(1.2)

A:

There are times you want to ask whether an object is an Exception (for example, when you get the result of a task back from a celery type process). You can do that using:
isinstance(x, Exception)

