# Python | Ways to sum list of lists and return sum list

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]
```

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