How Does 'in' Operator Work on List in Python

The in operator in Python

In Python, the in operator determines whether a given value is a constituent element of a sequence such as a string, array, list, or tuple.

When used in a condition, the statement returns a Boolean result of True or False. The statement returns True if the specified value is found within the sequence. When it is not found, we get a False.

In Python, a list is an ordered sequence that can hold several object types such as integer, character, or float. In other programming languages, a list is equivalent to an array. Square brackets are used to denote it, and a comma (,) is used to divide two things in the list.

Here we will see 3 different scenarios -

• Find One Item in Flat List

• Find the List in the Nested List

• Use of in with an if Statement

Assume we have taken a list containing random elements.

Example 1: Find One Item in Flat List

The following program checks whether the single element is present in the flat list or not using the in operator -

# input list
lst = ["Hello", 10, "TutorialsPoint", 20, "python", "code"]

# Checking if {TutorialsPoint} element in list using in operator
print("TutorialsPoint" in lst)

# Checking if {bigdata} element in list using in operator
print("bigdata" in lst)

Output

When you run the program, it will show this output -

True
False

As we can see from the output above, "TutorialsPoint" in the list evaluates to True. This indicates that the value "TutorialsPoint" can be found within the list. The term "bigdata" in the list evaluates to False. This means that the value "bigdata" was not found in the list.

Example 2: Find a List in a Nested List

The following program checks whether the given list is present in the nested list or not using the in operator:

# input list
lst = [["Hello", 10], ["TutorialsPoint", 20], ["python", "code"]]

# Checking if {TutorialsPoint,20} elements list present
print(["TutorialsPoint",20] in lst)

# Checking if {TutorialsPoint,code} elements list present 
print(["TutorialsPoint","code"] in lst)

Output

After running the program, you will get this result -

True
False

As we can see from the output above, ["TutorialsPoint",20] in the list evaluates to True. This indicates that the list ["TutorialsPoint",20] can be found within the list.

Despite the fact that both "TutorialsPoint" and "code" elements are nested here, it returns False because they are not in the same lists. They appear in various lists of the nested list.

Example 3: Use of in with an if Statement

The following program checks whether a single element is present in the flat list or not using the in operator.

# input list
lst = ["Hello", 10, "TutorialsPoint", 20, "python", "code"]

# Checking if {TutorialsPoint} element in list using in operator
if "TutorialsPoint" in lst:
   print('{TutorialsPoint} Element is in the given list')

# Checking if {bigdata} element in list using in operator
if "bigdata" in lst:
   print('{bigdata} Element is in the given list')

# If {bigdata} is not in list
else:
   print('{bigdata} Element is not present in the given list')

Output

This output will be displayed when the program runs:

{TutorialsPoint} Element is in the given list
{bigdata} Element is not present in the given list