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)
list: This contains a list of sorted integers.element: This provides an element that needs to be inserted into the sorted list.lo (Optional): Default is 0. It defines the starting position within the list for the search.hi (Optional): Default is len(list). It defines the ending position within the list for the search.key (Optional): If the 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:
bisect module, which contains methods like bisect_left, bisect_right, and so on.nums in a sorted order.ele to be inserted in the list nums.list and element as parameters to the bisect_left() method, which returns an 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.