In this Answer, we will learn about the `bisect_left()`

method in Python. Let’s start by looking at when we need this method.

We may want to insert an element in a sorted list, but we may still want to maintain the sort order after insertion. If we do this operation over a long list, this will become a costly operation. In this situation, we can use the ** bisect module**, which ensures that the list is automatically put in a sorted order.

The ** bisect_left() method** is provided by the

`bisect`

module, which returns the left-most index to insert the given element, while maintaining the sorted order.The syntax of the `bisect_left()`

function is given below:

```
import bisect
bisect.bisect_left(list, element, lo=0, hi=len(list), key=None)
```

: This contains a list of sorted integers.`list`

: This provides an element that needs to be inserted into the sorted list.`element`

(Optional): Default is 0. It defines the starting position within the list for the search.`lo`

(Optional): Default is`hi`

`len(list)`

. It defines the ending position within the list for the search.(Optional): If the`key`

`key`

parameter is None, the elements are compared directly without invoking any key function.

Let’s look at an example to better understand this.

#import the moduleimport bisect#given sorted list of numbersnums = [1,3,5,7,10,25,49,55]#given element to be inserted into the listele = 26#get index where to insert the elementidx = bisect.bisect_left(nums, ele)#print the indexprint(f"Insert element {ele} at index {idx} in nums list to maintain sorted order.")

In the code snippet above:

- On
**line 2**, we import the`bisect`

module, which contains methods like`bisect_left`

,`bisect_right`

, and so on. - On
**line 5**, we declare and initialize the list`nums`

in a sorted order. - On
**line 8**, we are given an element`ele`

to be inserted in the list`nums`

. - On
**line 11**, we pass`list`

and`element`

as parameters to the`bisect_left()`

method, which returns an index. - On
**line 14**, we print the returned index.

Let's see another code example for the `bisect_left()`

method with `hi`

and `lo`

parameters.

#import the moduleimport bisect#given sorted list of numbersnums = [1,3,5,7,10,25,49,55]#given element to be inserted into the listele = 26#get index where to insert the elementidx = bisect.bisect_left(nums, ele, lo=4, hi=len(nums))#print the indexprint(f"Insert element {ele} at index {idx} in nums list to maintain sorted order.")

On

**line 11**, the`bisect_left()`

function is used to find where the element`ele`

can be inserted into the sorted list`nums`

, starting the search from index`4`

(inclusive) and going up to the end of the list. The result is stored in the variable`idx`

.

Let's explore another code example utilizing the `bisect_left()`

method with the `key`

parameter for advanced list manipulation.

import bisect# List of tuples representing letters and corresponding integersletters = [(1, "a"), (3, "b"), (5, "c"), (7, "d"), (10, "e"), (25, "f"), (49, "g"), (55, "h")]# Extract the first element of each tuple (the integer)lambdafun = lambda x: x[0]# Search for the index where the value 6 should be insertedidx = bisect.bisect(letters, 6, key=lambdafun)print(f"Insert element 6 at index {idx} in letters list to maintain sorted order.")

On **line 7**, the `lambda`

is an anonymous function that takes one argument `x`

and returns the first element (`x[0]`

) of `x`

. For example, in our case, if `x`

is a tuple like `(1, "a")`

, then `x[0]`

would extract `1`

. This lambda function allows us to access the first element of each tuple when performing sorting on tuple elements.

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