Question 1

Why should you measure before optimizing performance?

Accepted Answer

Because the real bottleneck is rarely where we expect it, and optimizing without measuring adds complexity that may change nothing, or improves a part that is only a tiny share of the total time.

Question 2

What is the role of cProfile in performance analysis?

Accepted Answer

It records the number of calls of each function, the own time (tottime), and the cumulative time (cumtime), helping you identify the hot paths.

Question 3

When do you use collections.deque instead of list?

Accepted Answer

Use deque when you need to add or remove elements at both ends in O(1), such as queues and sliding windows, and use list for indexed access and appending at the end.

Question 4

When do generators improve memory use and when do they not improve time?

Accepted Answer

Generators lower peak memory use because they produce items on demand, but they do not necessarily speed up processing, and may be slower if you need to pass over the data several times.

Question 5

How do you use functools.lru_cache safely?

Accepted Answer

It stores function results by their arguments up to a limit (maxsize), and suits pure functions whose arguments are hashable and whose result does not depend on changing external state.

Question 6

Why is str.join usually preferred for assembling strings?

Accepted Answer

Because strings are immutable, repeated += in a loop can create a new string at each step at quadratic cost, whereas join computes the total size and builds the result once.

Question 7

How do you reduce the cost of inserting many rows into SQLite?

Accepted Answer

Batch the inserts into a single transaction and use executemany, instead of running a commit for every row.

Question 8

How do you deal with heavy object creation in a hot loop?

Accepted Answer

Measure first, then reduce unnecessary temporary objects, use built-in structures and functions written in C, or move the computation to NumPy or a compiled extension if the profiler shows the loop is the bottleneck.

Question 9

What does tracemalloc measure and how do you use it to find memory leaks?

Accepted Answer

tracemalloc tracks the memory allocations Python makes and where they happen in the code, and lets you take snapshots and compare them to see which lines' memory is growing.

Question 10

How does the choice of data structure change a program's performance?

Accepted Answer

The time complexity of the basic operations determines performance more than any other optimization: a membership check in a set or dict averages O(1), while in a list it is linear O(n), and this difference grows with data size.