Intersection of two list means we need to take all those elements which are common to both of the initial lists and store them into another list. Now there are various ways in Python, through which we can perform the Intersection of the lists.

Examples:

Input : lst1 = [15, 9, 10, 56, 23, 78, 5, 4, 9] lst2 = [9, 4, 5, 36, 47, 26, 10, 45, 87] Output : [9, 10, 4, 5] Input : lst1 = [4, 9, 1, 17, 11, 26, 28, 54, 69] lst2 = [9, 9, 74, 21, 45, 11, 63, 28, 26] Output : [9, 11, 26, 28]

**Method 1:**

This is the simplest method where we haven’t used any built-in functions.

`# Python program to illustrate the intersection ` `# of two lists in most simple way ` `def` `intersection(lst1, lst2): ` ` ` `lst3 ` `=` `[value ` `for` `value ` `in` `lst1 ` `if` `value ` `in` `lst2] ` ` ` `return` `lst3 ` ` ` `# Driver Code ` `lst1 ` `=` `[` `4` `, ` `9` `, ` `1` `, ` `17` `, ` `11` `, ` `26` `, ` `28` `, ` `54` `, ` `69` `] ` `lst2 ` `=` `[` `9` `, ` `9` `, ` `74` `, ` `21` `, ` `45` `, ` `11` `, ` `63` `, ` `28` `, ` `26` `] ` `print` `(intersection(lst1, lst2)) ` |

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*filter_none*

Output:

[9, 11, 26, 28]

**Method 2:**

This method includes the use of **set() method**.

`# Python program to illustrate the intersection ` `# of two lists using set() method ` `def` `intersection(lst1, lst2): ` ` ` `return` `list` `(` `set` `(lst1) & ` `set` `(lst2)) ` ` ` `# Driver Code ` `lst1 ` `=` `[` `15` `, ` `9` `, ` `10` `, ` `56` `, ` `23` `, ` `78` `, ` `5` `, ` `4` `, ` `9` `] ` `lst2 ` `=` `[` `9` `, ` `4` `, ` `5` `, ` `36` `, ` `47` `, ` `26` `, ` `10` `, ` `45` `, ` `87` `] ` `print` `(intersection(lst1, lst2)) ` |

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*filter_none*

Output:

[9, 10, 4, 5]

**Method 3:**

In this method we **set() the larger list** and then use the built-in function called **interscetion()** to compute the intersected list. **intersection()** is a first-class part of set.

`# Python program to illustrate the intersection ` `# of two lists using set() and intersection() ` `def` `Intersection(lst1, lst2): ` ` ` `return` `set` `(lst1).intersection(lst2) ` ` ` `# Driver Code ` `lst1 ` `=` `[ ` `4` `, ` `9` `, ` `1` `, ` `17` `, ` `11` `, ` `26` `, ` `28` `, ` `28` `, ` `26` `, ` `66` `, ` `91` `] ` `lst2 ` `=` `[` `9` `, ` `9` `, ` `74` `, ` `21` `, ` `45` `, ` `11` `, ` `63` `] ` `print` `(Intersection(lst1, lst2)) ` |

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*filter_none*

Output:

{9, 11}

**Method 4:**

By the use of this **hybrid method** the complexity of the program falls to O(n). This is an efficient way of doing the following program.

`# Python program to illustrate the intersection ` `# of two lists ` `def` `intersection(lst1, lst2): ` ` ` ` ` `# Use of hybrid method ` ` ` `temp ` `=` `set` `(lst2) ` ` ` `lst3 ` `=` `[value ` `for` `value ` `in` `lst1 ` `if` `value ` `in` `temp] ` ` ` `return` `lst3 ` ` ` `# Driver Code ` `lst1 ` `=` `[` `9` `, ` `9` `, ` `74` `, ` `21` `, ` `45` `, ` `11` `, ` `63` `] ` `lst2 ` `=` `[` `4` `, ` `9` `, ` `1` `, ` `17` `, ` `11` `, ` `26` `, ` `28` `, ` `28` `, ` `26` `, ` `66` `, ` `91` `] ` `print` `(intersection(lst1, lst2)) ` |

*chevron_right*

*filter_none*

Output:

[9, 9, 11]

**Method 5:**

This is the where the intersection is performed over sub-lists inside other lists. Here we have used the concept of **filter().**

`# Python program to illustrate the intersection ` `# of two lists, sublists and use of filter() ` `def` `intersection(lst1, lst2): ` ` ` `lst3 ` `=` `[` `list` `(` `filter` `(` `lambda` `x: x ` `in` `lst1, sublist)) ` `for` `sublist ` `in` `lst2] ` ` ` `return` `lst3 ` ` ` `# Driver Code ` `lst1 ` `=` `[` `1` `, ` `6` `, ` `7` `, ` `10` `, ` `13` `, ` `28` `, ` `32` `, ` `41` `, ` `58` `, ` `63` `] ` `lst2 ` `=` `[[` `13` `, ` `17` `, ` `18` `, ` `21` `, ` `32` `], [` `7` `, ` `11` `, ` `13` `, ` `14` `, ` `28` `], [` `1` `, ` `5` `, ` `6` `, ` `8` `, ` `15` `, ` `16` `]] ` `print` `(intersection(lst1, lst2)) ` |

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*filter_none*

**Working: **The filter part takes each sublist’s item and checks to see if it is in the source list. The list comprehension is executed for each sublist in list2.

Output:

[[13, 32], [7, 13, 28], [1, 6]]

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