Bisect Left in Python with Code Examples
Bisect left is a function in Python that helps you insert items into a sorted list. It adds the item to the list such that the list stays sorted. This is a useful function if you perform binary searches or want to insert an item into a long list without having to sort the list again.
The bisect left function takes two parameters:
 List: The list where we want to insert the item.
 Item: The item that we want to insert.
The function will then return the position where we should insert the item in the list. Here’s an example:
import bisect
list1 = [1, 2, 3, 4, 5]
print(bisect.bisect_left(list1, 3))
Output:
2
So, in this example, we’re inserting the item “3” into the list [1, 2, 3, 4, 5]. The bisect left function tells us that “3” should be inserted at position 2 in the list.
If we use the bisect right function instead, we’ll get a different result:
import bisect
list1 = [1, 2, 3, 4, 5]
print(bisect.bisect_right(list1, 3))
Output:
3
The bisect right function tells us that “3” should be inserted at position 3 in the list. This is because the bisect right function inserts the item to the right of any existing items that are equal to it.
Here’s another example of how we can use bisect left to insert items into a list:
import bisect
def bin_search(arr, n):
pos = bisect.bisect_left(arr, n)
return pos
arr = [1, 3, 5, 6]
print("List: ", arr)
print("Item 4 found at index:", bin_search(arr, 4))
Output:
List: [1, 3, 5, 6]
Item 4 found at index: 2
In this example, we first define a function named bin_search that takes two parameters: arr (the array we want to insert into) and n (the item we want to insert). The function then uses the bisect left function to find the position where n should be inserted into arr.
We then define an array named arr and print it to the console. Finally, we call the bin_search function with the parameters arr and 4 and print the result to the console.
The bisect left function is very useful if you’re dealing with large, sorted lists. It can help you insert items into the list quickly and efficiently, without having to sort the list again. Additionally, the function is easy to use and can be incorporated into your Python code easily.
here's some additional information about the previous topics:
Binary Search:
Binary search is an algorithmic technique that is used to find a specific item in a sorted list. It's a very efficient search algorithm with a time complexity of O(log n) in the worst case scenario. Binary search works by repeatedly dividing the sorted list in half and comparing the target item with the middle element in the list. Based on the comparison, the algorithm either continues the search on the left half or right half of the list until the item is found or all elements have been checked.
While binary search is very efficient, it must be used on sorted lists only. If the list is not sorted, binary search may not yield accurate results. In Python, you can implement binary search using a loop or recursive function. Here's an example of a binary search implementation using a loop:
def binary_search(arr, target):
first = 0
last = len(arr)  1
while first <= last:
mid = (first + last) // 2
if arr[mid] == target:
return mid
elif arr[mid] > target:
last = mid  1
else:
first = mid + 1
return 1
arr = [2, 4, 6, 8, 10, 12]
target = 8
result = binary_search(arr, target)
if result != 1:
print("Element is present at index", str(result))
else:
print("Element is not present in array")
Bisect Right:
Bisect right is similar to bisect left, except it returns the index at which the target item should be inserted in a sorted list to the right of any existing items that are equal to it. Here's an example of bisect right in Python:
import bisect
def insert_into_list(arr, target):
index = bisect.bisect_right(arr, target)
arr.insert(index, target)
return arr
arr = [1, 3, 4, 5, 7, 9]
target = 6
new_arr = insert_into_list(arr, target)
print(new_arr)
Output:
[1, 3, 4, 5, 6, 7, 9]
In this example, we define a function named insert_into_list which takes two parameters: arr (the list we want to insert into) and target (the item we want to insert). The function then uses bisect right to find the position where the target item should be inserted in the list. Finally, the function uses the insert method to insert the item into the list at the correct position and returns the modified list.
Popular questions

What is bisect left in Python?
Answer: Bisect left is a Python function that helps you insert items into a sorted list while keeping the list in order. 
How many parameters does bisect left take?
Answer: Bisect left takes two parameters – the list where we want to insert the item and the item itself. 
What does bisect left return?
Answer: Bisect left returns the index or position where we should insert the item in the list so that the list remains sorted. 
What is the time complexity of bisect left?
Answer: The time complexity of bisect left in Python is O(log n), where n is the number of elements in the list. 
Can bisect left be used for unsorted lists?
Answer: No, bisect left can only be used for sorted lists. If the list is not sorted, bisect left may not yield accurate results.
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