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.

From PEP 8, in the “Programming Recommendations” section:

For sequences, (strings, lists, tuples), use the fact that empty sequences are false.

So you should use:

if not some_string:

or:

if some_string:

Just to clarify, sequences are evaluated to False or True in a Boolean context if they are empty or not. They are not equal to False or True.

The most elegant way would probably be to simply check if its true or falsy, e.g.:

if not my_string:

However, you may want to strip white space because:

 >>> bool("")
 False
 >>> bool("   ")
 True
 >>> bool("   ".strip())
 False

You should probably be a bit more explicit in this however, unless you know for sure that this string has passed some kind of validation and is a string that can be tested this way.

I would test noneness before stripping. Also, I would use the fact that empty strings are False (or Falsy). This approach is similar to Apache's StringUtils.isBlank or Guava's Strings.isNullOrEmpty

This is what I would use to test if a string is either None OR empty OR blank:

def isBlank (myString):
    return not (myString and myString.strip())

And the exact opposite to test if a string is not None NOR empty NOR blank:

def isNotBlank (myString):
    return bool(myString and myString.strip())