Python: Empty String?

by Scott Hebert

Python logo -rightI've mentioned before that empty strings in Python are false. This leads to a common if not string paradigm. Unfortunately, this can be problematic. Check out this snippet:

That pretty much worked out just as we imagined. The empty string returned False and our code did what it was supposed to. When we start running into a problem is when our string isn't really a string. For example:

In this case, our string is now a None object. We may have done this on purpose or it could have been a mistake. A common scenario is that a function returned a None object when we expected a string. What we find is that None, False, 0, and "" are all equivalent, and in the paradigm of checking for an empty string with if not string, empty.

For quick and dirty scripts, if not string works just fine. Small bits of code where you know exactly what the input is going to look like or one-off scripts that need some basic error-checking are not usually an issue. For more complicated code, the answer is better error-checking before getting to if not string. For example, if a function can return a None object for some reason, that's a condition that should be checked for when the function returns. In my experience, you can expect to run into this often when working with third-party APIs.