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# Find size of a list in Python

A list is a collection data type that is ordered and changeable. A list can have duplicate entries as well. Here, the task is to find the number of entries in a list in Python.

Examples:

`Input: a = [1, 2, 3, 1, 2, 3]Output: 6Explanation: The output is 6 because the number of entries in the list a is also 6.`

# Find the Length of a List in Python

### Find the size of the list using the len() method

The len() works in O(1) time as the list is an object and has a member to store its size. Below is a description of len() from Python docs.

Return the length (the number of items) of an object. The argument may be a sequence (such as a string, bytes, tuple, list, or range) or a collection (such as a dictionary, set, or frozen set).

## Python3

 `# Python program to demonstrate working of len()``a ``=` `[]``a.append(``"Hello"``)``a.append(``"Geeks"``)``a.append(``"For"``)``a.append(``"Geeks"``)``print``(``"The length of list is: "``, ``len``(a))`

Output

```The length of list is:  4

```

### Find the length of a list using the sum() function

Another approach is to use the built-in sum() function in combination with a generator expression. This allows you to find the size of a list by summing the number of elements in the list that meet a certain condition.

## Python3

 `# list of numbers``numbers ``=` `[``1``, ``2``, ``3``, ``1``, ``2``, ``3``]` `# find the size of the list``size ``=` `sum``(``1` `for` `num ``in` `numbers)` `# print the size of the list``print``(size)`

Output

```6

```

This will output 6 because the list contains 6 elements.

Time complexity: The time complexity of the approach using the sum() function and a generator expression is O(n), where n is the length of the list.
Space complexity: The auxiliary space complexity of this approach is O(1) because the generator expression only requires a single variable to store the current element being processed.

### Find the length of the list using for loop

In this way, we initialize a variable count and then we increment the variable through the loop, and by the end of the loop we get the length of the list in our count variable.

## Python3

 `lst ``=` `[``1``,``1``,``2``,``5``,``1``,``5``,``2``,``4``,``5``]``count ``=` `0``for` `i ``in` `lst:``  ``count ``+``=` `1``print``(``"The length of the lst is :"``,count)`

Output

```The length of the lst is : 9

```

Time Complexity: O(n)
Space Complexity: O(1)

### Find the size of the list using the `length_hint()` method

The `length_hint()` function from the `operator` module to estimate the length of a list. However, please note that this function is not guaranteed to give you the exact size of the list, especially for standard Python lists.

The `length_hint()` the function provides a hint about the expected length of an iterable, but it might not be accurate for all types of iterables. Here’s your example:

## Python3

 `from` `operator ``import` `length_hint` `lst ``=` `[``'Geeks'``, ``'For'``, ``'Geeks'``]``size ``=` `length_hint(lst)``print``(``'The size of the size lst:'``,size)`

Output

```The size of the size lst: 3

```

Time Complexity: O(n)
Space Complexity: O(1)