How to Check If a List Is Empty

How do I check if a list is empty?

if not a:
    print("List is empty")

Using the implicit booleanness of the empty list is quite pythonic.

What is the quickest way to check if a list is empty, and in what scenarios would one method be preferred over the other?

It's simplest to just use the implicit boolean method of lists:

if mylist: will branch True if mylist has contents, and False if mylist is empty. From the documentation, an empty list is considered to be False as in boolean evaluation the default __len__() method is called and it is equal to zero. This is the most pythonic and the fastest way to evaluate it, though mechanistically identical to if len(mylist) == 0:. The same applies to strings, tuples, lists, dictionaries, sets, and range().

Edit: With regards to one of the given examples, as noted by @Carcigenicate, any() will fail in select situations if the goal is purely to check if a list is empty. any() will return False "if the list is non-empty and contains only Falsey elements."

For example, any([False, 0]) will return False despite the list containing two objects.

How to check if a list is empty

You can use a function that recursively checks the items within sublists:

def is_empty(l):
    return all(is_empty(i) if isinstance(i, list) else False for i in l)

so that:

print(is_empty([[], [], [[], []]]))
print(is_empty([[], [], [[], [1]]]))

outputs:

True
False

And if you want to handle lists that contain circular references you can use a seen set to keep track of the list references the function has seen and skip them when they are seen:

def is_empty(l, seen=None):
    if seen is None:
        seen = set()
    return all(seen.add(id(i)) or is_empty(i, seen) if isinstance(i, list) else False for i in l if id(i) not in seen)

so that:

a = []
a.append(a)
print(is_empty(a))
a = [1]
a.append(a)
print(is_empty(a))

outputs:

True
False

How to check if a list is empty in Python?

if not myList:
  print "Nothing here"

Python: condition to check that none of list's element is an empty list

Since an non-empty list is considered truthy, you can use all:

if all(A):
    print("No empty list in A")
else:
    print("At least one empty list in A")

How to check if a list has both empty and non-empty values in python

list = ["Efsf","efsfs",""]
list1 = ["",'']
list2 =  ["fsef",5 ,5]

def check(list):
    null =''
    if null in list and len(list)-list.count(null)>0:
        print("List has both empty and non-empty values.")
    else:
        print("List does not have both empty and non-empty values.")
check(list)
check(list1)
check(list2)

output:

List has both empty and non-empty values.

List does not have both empty and non-empty values.

List does not have both empty and non-empty values.

Two ways to check if a list is empty - differences?

The first tells you whether the list variable has been assigned a List instance or not.

The second tells you if the List referenced by the list variable is empty.
If list is null, the second line will throw a NullPointerException.

If you want to so something only when the list is empty, it is safer to write :

if (list != null && list.isEmpty()) { do something }

If you want to do something if the list is either null or empty, you can write :

if (list == null || list.isEmpty()) { do something }

If you want to do something if the list is not empty, you can write :

if (list != null && !list.isEmpty()) { do something }

Checking for empty or null List<string>

Try the following code:

 if ( (myList!= null) && (!myList.Any()) )
 {
     // Add new item
     myList.Add("new item"); 
 }

A late EDIT because for these checks I now like to use the following solution.
First, add a small reusable extension method called Safe():

public static class IEnumerableExtension
{       
    public static IEnumerable<T> Safe<T>(this IEnumerable<T> source)
    {
        if (source == null)
        {
            yield break;
        }

        foreach (var item in source)
        {
            yield return item;
        }
    }
}

And then, you can do the same like:

 if (!myList.Safe().Any())
 {
      // Add new item
      myList.Add("new item"); 
 }

I personally find this less verbose and easier to read. You can now safely access any collection without the need for a null check.

And another EDIT, which doesn't require an extension method, but uses the ? (Null-conditional) operator (C# 6.0):

if (!(myList?.Any() ?? false))
{
    // Add new item
    myList.Add("new item"); 
}

How check if the lists in a list are not empty?

You can use stream API for this, but also a plain loop too:

 boolean allNonEmptyOrNull = myList.stream()
     .allMatch(x -> x != null && !x.isEmpty());

Or you can check if null is contained or an an empty List for example, via:

System.out.println(myList.contains(null) || myList.contains(Collections.<Integer> emptyList()));

But this last option will break with Java 9 immutable collections, for example:

List.of(1, 2, 3).contains(null); 

will throw a NullPointerException.

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