# Python | Print all the common elements of two lists

• Difficulty Level : Easy
• Last Updated : 17 Jan, 2023

Given two lists, print all the common elements of two lists.

Examples:

```Input : list1 = [1, 2, 3, 4, 5]
list2 = [5, 6, 7, 8, 9]
Output : {5}
Explanation: The common element of the lists is 5.

Input : list1 = [1, 2, 3, 4, 5]
list2 = [6, 7, 8, 9]
Output : No common elements
Explanation: They do not have any
elements in common in between them```

### Method 1:Using Set’s & property

Convert the lists to sets and then print set1&set2. set1&set2 returns the common elements set, where set1 is the list1 and set2 is the list2.
Below is the Python3 implementation of the above approach:

## Python3

 `# Python program to find the common elements``# in two lists``def` `common_member(a, b):``    ``a_set ``=` `set``(a)``    ``b_set ``=` `set``(b)` `    ``if` `(a_set & b_set):``        ``print``(a_set & b_set)``    ``else``:``        ``print``(``"No common elements"``)``         ` ` ` `a ``=` `[``1``, ``2``, ``3``, ``4``, ``5``]``b ``=` `[``5``, ``6``, ``7``, ``8``, ``9``]``common_member(a, b)`` ` `a ``=` `[``1``, ``2``, ``3``, ``4``, ``5``]``b ``=` `[``6``, ``7``, ``8``, ``9``]``common_member(a, b)`

Output:

```{5}
No common elements```

### Method 2:Using Set’s intersection property

Convert the list to set by conversion. Use the intersection function to check if both sets have any elements in common. If they have many elements in common, then print the intersection of both sets.
Below is the Python3 implementation of the above approach:

## Python3

 `# Python program to find common elements in``# both sets using intersection function in``# sets`  `# function``def` `common_member(a, b):   ``    ``a_set ``=` `set``(a)``    ``b_set ``=` `set``(b)``    ` `    ``# check length``    ``if` `len``(a_set.intersection(b_set)) > ``0``:``        ``return``(a_set.intersection(b_set)) ``    ``else``:``        ``return``(``"no common elements"``)``    ` ` ` `a ``=` `[``1``, ``2``, ``3``, ``4``, ``5``]``b ``=` `[``5``, ``6``, ``7``, ``8``, ``9``]``print``(common_member(a, b))`` ` `a ``=``[``1``, ``2``, ``3``, ``4``, ``5``]``b ``=``[``6``, ``7``, ``8``, ``9``]``print``(common_member(a, b))`

Output:

```{5}
No common elements```

Method 3 : Using for loop

## Python

 `def` `common_member(a, b):``    ``result ``=` `[i ``for` `i ``in` `a ``if` `i ``in` `b]``    ``return` `result` `a ``=` `[``1``, ``2``, ``3``, ``4``, ``5``]``b ``=` `[``5``, ``6``, ``7``, ``8``, ``9``]` `print``(``"The common elements in the two lists are: "``)``print``(common_member(a, b))`

Output:

```The common elements in the two lists are:
[5]```

#### Method 4: Using collections

This code uses the collections module to create two Counter objects from the two lists, a and b. The & operator is then used to return the common elements from the two lists. The result is then printed out.

## Python3

 `import` `collections` `def` `common_member(a, b):``    ``result ``=` `collections.Counter(a) & collections.Counter(b)``    ``return` `result.keys()`` ` `a ``=` `[``1``, ``2``, ``3``, ``4``, ``5``]``b ``=` `[``5``, ``6``, ``7``, ``8``, ``9``]`` ` `print``(``"The common elements in the two lists are: "``)``print``(common_member(a, b))`

Output

```The common elements in the two lists are:
dict_keys([5])```

Method 5: Using operator.countOf()

## Python3

 `import` `operator as op``def` `common_member(a, b):``    ``result ``=` `[i ``for` `i ``in` `a ``if` `op.countOf(b,i)>``0` `]``    ``return` `result` `a ``=` `[``1``, ``2``, ``3``, ``4``, ``5``]``b ``=` `[``5``, ``6``, ``7``, ``8``, ``9``]` `print``(``"The common elements in the two lists are: "``)``print``(common_member(a, b))`

Output

```The common elements in the two lists are:
[5]```

Time Complexity: O(N)

Auxiliary Space : O(N)

My Personal Notes arrow_drop_up