Find common elements in two lists in python

Find common elements in two lists Python

💡 Outline
You can first convert first list into set using set() and call intersection() by passing second list as parameter to find common element in two lists in Python.

In this tutorial, we will see different methods to find common elements in two lists in python.

Using the intersection() Function

This is the easiest method to find common elements in two lists in Python. As the name suggests, the intersection() function is a built-in python function that is used to return a set that contains the elements which are common in two sets. The sets can be of any form i.e a list or a dictionary.

Example:

Output:

{10, 20, 30}

Note that, __name__ variable is used in the above code. It is a built-in variable that is used to see whether the current code is being run on its own or an external module is being imported from somewhere. Thus, the __name__ variable checks the name of the current module in the ongoing code. It is usually used with an if statement and where it is assigned to '__main__' when there is no module in the program. Otherwise, __name__ is assigned to the name of the module used in the program.

Using List Comprehension

List Comprehension is a very concise way which helps in creating a list based on values stored from existing list or lists. This is also one way of finding common elements from two lists.

Example:

Output:

[10, 20, 30]

NOTE: There is one drawback in using this method to find common elements i.e this method should not be used in the case of large lists.

Using & Operator

The set’s & operator is also one way of finding common elements in two lists. In this method, both the lists are converted into sets first and then the common elements are found using &.

Example:

Output:

{10, 20, 30}
There are no common elements

Explantion

  • First both the lists are converted into set using set() function.
  • Used & to find common elements in two sets in Python.
  • We have used def keyword in above code. def` is used to define a function with more than one statement in a function. This function can be called with the help of the function name at the end of the code. In the above code, we have called the function twice at the end where we made two cases of the sets to find the common elements, one with some common elements and one with no common elements.

That’s all about how to find common elements in two lists in Python.

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