The list is an important container and used almost in every code of day-day programming as well as web-development, more it is used, more is the requirement to master it and hence knowledge of its operations is necessary. Given a list of lists, the program to suppose to return the sum as the final list.

Let’s see some of the methods to sum a list of list and return list.

**Method # 1:** Using Naive method

`# Python code to demonstrate` `# sum of list of list` `# using naive method` ` ` `# Declaring initial list of list` `L ` `=` `[[` `1` `, ` `2` `, ` `3` `],` ` ` `[` `4` `, ` `5` `, ` `6` `],` ` ` `[` `7` `, ` `8` `, ` `9` `]]` ` ` `# Printing list of list` `print` `(` `"Initial List - "` `, ` `str` `(L))` ` ` `# Using naive method` `res ` `=` `list` `()` `for` `j ` `in` `range` `(` `0` `, ` `len` `(L[` `0` `])):` ` ` `tmp ` `=` `0` ` ` `for` `i ` `in` `range` `(` `0` `, ` `len` `(L)):` ` ` `tmp ` `=` `tmp ` `+` `L[i][j]` ` ` `res.append(tmp)` ` ` `# printing result` `print` `(` `"final list - "` `, ` `str` `(res))` |

**Output:**

Initial List - [[1, 2, 3], [4, 5, 6], [7, 8, 9]] final list - [12, 15, 18]

**Method #2: **Using numpy array

A numpy is a general-purpose array-processing package. It provides a high-performance multidimensional array object, and tools for working with these arrays.

`# Python code to demonstrate` `# sum of list of list` `# using numpy array functions` `import` `numpy as np` ` ` `# Declaring initial list of list` `List` `=` `np.array([[` `1` `, ` `2` `, ` `3` `],` ` ` `[` `4` `, ` `5` `, ` `6` `],` ` ` `[` `7` `, ` `8` `, ` `9` `]])` ` ` `# Printing list of list` `print` `(` `"Initial List - "` `, ` `str` `(` `List` `))` ` ` `# Using numpy sum` `res ` `=` `np.` `sum` `(` `List` `, ` `0` `)` ` ` `# printing result` `print` `(` `"final list - "` `, ` `str` `(res))` |

**Output:**

Initial List - [[1 2 3] [4 5 6] [7 8 9]] final list - [12 15 18]

**Method #3:** Using `zip()`

and list comprehension

`# Python code to demonstrate` `# sum of list of list using ` `# zip and list comprehension` ` ` `# Declaring initial list of list` `List` `=` `[[` `1` `, ` `2` `, ` `3` `],` ` ` `[` `4` `, ` `5` `, ` `6` `],` ` ` `[` `7` `, ` `8` `, ` `9` `]]` ` ` `# Printing list of list` `print` `(` `"Initial List - "` `, ` `str` `(` `List` `))` ` ` `# Using list comprehension` `res ` `=` `[` `sum` `(i) ` `for` `i ` `in` `zip` `(` `*` `List` `)]` ` ` `# printing result` `print` `(` `"final list - "` `, ` `str` `(res))` |

**Output:**

Initial List - [[1, 2, 3], [4, 5, 6], [7, 8, 9]] final list - [12, 15, 18]

Attention geek! Strengthen your foundations with the **Python Programming Foundation** Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the **Python DS** Course. And to begin with your Machine Learning Journey, join the **Machine Learning – Basic Level Course**