How to Check if an Element is in a List in Python

A “List” is a built-in data structure in Python that stores all kinds of data (numerical as well as categorical). While working with large Lists in Python, sometimes it becomes difficult to check if the list contains a particular item or not. Therefore, Python offers numerous ways to deal with such scenarios without any hassles.

The method for determining the existence/availability of an element in a list will be discussed in this Python blog.

How to Check Whether a Python Element is in a List?

The below-listed methods will be discussed step-by-step to check the existence of an element in a List:

• Using IN Operator
• Using for Loop
• Using any()
• Using Count()
• Using Counter()
• Using Try-Except()
• Using find()

Method 1: Use IN Operator to Check Existence/Availability of an Element in a Python List

Using the “in” operator to check if an element is present in the list is a straightforward approach. The element must be present in the list for the function to return True. For instance,

list1 = ["Harry", "Ron", "Adam", "Steve", "Micheal"]

if 'Ron' in list:
    print (" 'Ron' is found in the list1")
else:
    print (" 'Ron' is not found in the list1")

if 'Jesse' in list:
    print (" 'Jesse' is found in the list1")
else:
    print (" 'Jesse' is not found in the list1")

In the above code:

• A list is initialized which contains 5 names.
• The code checks to see if the string “Ron” is in the list using the if statement and the IN operator. 
• If “Ron” is listed, it will say “Ron is present in the list”; otherwise, it will say “Ron” is not listed.
• Similarly, if “Jesse” exists in the list, it prints “Jesse” is found in the list; otherwise, it will print “Jesse” is not found in the list.

Output

As “Ron” exists in the list it’s printed. Jesse doesn’t exist so it’s not printed.

Method 2: Use for Loop to Check if an Element Exists in a List

A for loop can also be implemented to determine whether an element is included/present in a list or not. The loop will repeatedly iterate through the list, checking for the element. It will stop if there’s a match.

Here’s an example:

names = ["Harry", "Ron", "Adam", "Steve", "Micheal"]
for i in names:
    if i == 'Steve':
        print ("Found the element")

In the above code:

• A list is initialized.
• A for loop is used which iterates through the list and checks for a match.
• If “Steve” is listed, it will say “Found the element”, otherwise it will say “Element not found”.

The output of the above code is as follows:

It can be seen that Steve is present in the list, hence the program says “Found the element”

Method 3: Use any() to Check if an Element Exists in a List

To check if at least one element in an iterable is evaluated to “True” any(), a built-in function in Python is used. For instance, in the following code, each list element is compared to a string to see if there’s a match:

list1 = ["Harry", "Ron", "Adam", "Steve", "Micheal"]
string = "Micheal lives in San Francisco"

print ("The original string is: " + string)
print ("The original list is: " + str(list1))
resultant_val = any(item in string for item in list1)
print ("Does the string contain 'Micheal': " + str(resultant_val))

In the above code:

• A list and a string are defined.
• The code then prints out the original string and list using the print function. The str method is used to transform the list into a string.
• The code uses the list comprehension and any() function to check if any item from list1 is present in the given string. It iterates through the list using the “in” operator to check if each item is a substring of a string.
• Finally, if the given element is present in the list, it returns True, otherwise False

The output of the above code is as follows:

As Micheal is present in the list, the code returns true.

Method 4: Use Count() to Check if an Element Exists/Present in a List

Count() is a built-in method that returns how many times the provided element appears in the list. 

list1 = ["Harry", "Ron", "Adam", "Steve", "Micheal"]

result = list1.count("Steve")

if result > 0:
    print("Steve exists in the list")
else:
    print("Steve does not exist in the list")

In the above code:

• A list is defined named “list1”.
• The code uses the list.count() method to check how many times the name “Steve” appears in the list.
• The if statement is then used in the code to determine whether the result(count) is larger than 0.
• If result< 0, it means “Steve” exists in the list and if the result =0, it means Steve doesn’t exist in the list.

Below is a display of the code’s output:

As the result >0, Steve exists in the list.

Method 5: Use Counter() to Check if an Element Exists/Available in a List

The Counter() method creates a frequency dictionary that counts the existence of each element in the list. It is not a built-in method so we have to import the Counter class from the Collections module.

from collections import Counter

list1 = ["Harry", "Ron", "Adam", "Steve", "Micheal"]

frequency = Counter(list1)
if(frequency["Harry"] > 0):
    print("Yes, Harry exists in list")
else:
    print("No, Harry does not exists in list")

In the above code:

• The Collections module counter class is imported.
• A list is defined named “list1”.
• The code uses the counter() method to create a frequency dictionary that counts the occurrence of each element in the list1.
• The code then uses an if statement to check if the count of Harry in the frequency dictionary is greater than 0.
• If the count>0, it means Harry is present in the list1 otherwise Harry doesn’t exist in the list.

The above code displays the output shown below:

From the above code screenshot, we can see that Harry exists in the list.

Method 6: Using Try-Except Block to Check if an Element Exists in a List

We can use exception handling to manually raise exceptions if the element exists in the list. An example is shown below:

def element_exists(lst, element):
  try:
    lst.index(element)
    return True
  except ValueError:
    return False

list1 = ["Harry", "Ron", "Adam", "Steve", "Micheal"]

print(element_exists(list1, "Ron"))
print(element_exists(list1, "Joseph"))

In the above code:

• The element_exists function is initialized which takes 2 parameters, lst, and element.
• Inside this function, there is a try block that attempts to find the index of the specified element using the index method.
• The function returns True which means that element exists in the list.
• The function returns False if the element is not found in the list( the ValueError exception is  raised ), and the code inside the except block is executed
• Outside the function, a list named list1 is defined.
• The code then calls the function twice to see that “Ron” and “Joseph” exist in the list.

The above code displays the following output.

It displayed True because Ron is present in the list while it displayed False because Joseph doesn’t exist in the list.

Method 7: Use find() to Test the Existence/Availability of an Element in a List

find() is used to determine where in a given string the substring appears or not. Let’s implement this method practically as shown below:

list1 = ["Harry", "Ron", "Adam", "Steve", "Micheal"]
print("Checking if Steve exists in list")
x=list(map(str,list1))
y="-".join(x)

if y.find("Steve") !=-1:
    print("Yes, Steve exists in list")
else:
    print("No, Steve does not exists in list")

In the above code:

• A list is defined named list1.
• The code uses the map function to convert the elements in list1 into string and stores the result in the variable x.
• The x-list components in the code are concatenated with hyphens using the join method.
• To search for the substring “Steve” within the y string, the find() function is utilized.
• If Steve is found in the y string, the find() function returns an index other than -1 and prints “Steve exists in the list”. If Steve is not found in the y string, the find() function returns an index of -1 and prints (“Steve doesn’t exist in the list).

The above code results in the output shown below:

It can be seen that Steve exists in the list.

Conclusion

There are numerous methods in Python to verify whether an element exists in the list or not. We can use the “in” operator, “for” loop, “any()” method, “find()”, “count()”, “counter()”, “try-except” block method, etc. This guide has illustrated various methods to determine whether an element is present in a list in Python.