How to check if the string is empty?

Empty strings are “falsy” (python 2 or python 3 reference), which means they are considered false in a Boolean context, so you can just do this:

if not myString:

This is the preferred way if you know that your variable is a string. If your variable could also be some other type then you should use:

if myString == "":

See the documentation on Truth Value Testing for other values that are false in Boolean contexts.