How to check if the string is empty?

Question

Does Python have something like an empty string variable where you can do:

if myString == string.empty:

Regardless, what's the most elegant way to check for empty string values? I find hard coding "" every time for checking an empty string not as good.

Solution 1

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

Solution 2

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.

Solution 3

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.

Solution 4

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):
    if myString and myString.strip():
        #myString is not None AND myString is not empty or blank
        return False
    #myString is None OR myString is empty or blank
    return True

And, the exact opposite to test if a string is not None NOR Empty NOR Blank:

def isNotBlank (myString):
    if myString and myString.strip():
        #myString is not None AND myString is not empty or blank
        return True
    #myString is None OR myString is empty or blank
    return False

More concise forms of the above code:

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

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

Solution 5

I once wrote something similar to Bartek's answer and javascript inspired:

def is_not_blank(s):
    return bool(s and not s.isspace())

Test:

print is_not_blank("")    # False
print is_not_blank("   ") # False
print is_not_blank("ok")  # True
print is_not_blank(None)  # False

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