Insert before equal values while keeping a list sorted.
What You Will Learn
insort_left(list, item) mutates the list in place, using the left insertion point. It returns None, and insertion still costs O(n) due to shifting.
Time complexity assumes a specific input structure. Include setup work such as sorting or building a lookup table when comparing complete solutions.
Step-by-Step Example
The example below makes the behavior visible with small input values that you can change safely.
from bisect import insort_left
values = [1, 3, 3, 7]
insort_left(values, 3)
print(values)How the Example Works
- The imports provide the standard-library tools used in the demonstration: bisect.
- The variable values holds the result of [1, 3, 3, 7]. Later lines use that value or inspect how it changes.
- The print() calls make the return values or state visible so you can compare them with the explanation and check your prediction.
For the chosen input, the expression values prints [1, 3, 3, 3, 7]. Compare that result with the rule above before you change the argument.
Expected output from the example:
[1, 3, 3, 3, 7]When You Would Use This
This technique matters when a program handles larger queues, sorted records, or repeated lookups. Choose the data structure based on actual operations and the preconditions the algorithm requires. Verify boundary inputs before optimizing for speed.
Practice: Modify the Code
Insert several scores into a previously sorted list.
Verify the changed output against the behavior described above, including the relevant invalid or boundary case.
For complete parameters and version details, consult the official Python documentation.
Common Beginner Mistakes
- Assigning the return value from insort_left(), which is None, instead of using the modified list.
- Assuming the input is correctly sorted or arranged without checking the algorithm’s preconditions.
Key Takeaways
- Insert before equal values while keeping a list sorted.
- insort_left(list, item) mutates the list in place, using the left insertion point.
- Apply this operation only after checking the assumptions and input conditions shown in the example.