🦥 Profilers For Dummies

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Profilers For Dummies

Every developer will encounter this situation one day:

You write some code, it works and you’re proud!

But… It’s super slow.

Now you stare at the code and suffer in silence because you have no idea what’s wrong.

This is where where profilers come in.

What’s a Profiler?

A profiler is a tool that tells you exactly where your program is spending its resources: time, CPU, or memory.

Think of it like a fitness tracker for your code.

Fitness trackers don’t just say you did exercise, It shows what type of exercise:

• You spent 20% of your run walking,

• 10% climbing stairs,

• 30% sitting on the couch,

• and 40% scrolling TikTok.

For code, this means you can see:

• Which functions are running the most

• How much CPU they burn each call

• Whether you’re allocating memory and never giving it back

• How long your program sits around waiting for a database or network

A profiler doesn’t just tell you something is slow, it shows you where and why.

Types of Profilers (and when you’d use them)

I’ll be using Python (as usual) since it’s easier to understand the examples.

CPU Profilers

Use case: Your app works but it feels slow. Are you looping too much? Sorting data inefficiently? CPU profilers help by showing you where the program is spending the most time.

# cpu_example.py
import time

def slow_function():
    time.sleep(3)


def fast_function():
    sum(range(1000000))

slow_function()
fast_function()

Run with Python’s built-in CPU profiler:

python -m cProfile cpu_example.py

Output example

Memory Profilers

These track memory allocation over time.

Use case: Your app starts fine but slows down after an hour… or crashes with “out of memory.” Memory profiling helps you catch leaks.

# memory_exmple.py
from memory_profiler import profile

@profile
def my_func():
    a = [1] * (10 ** 6)
    b = [2] * (2 * 10 ** 7)
    del b
    return a

if __name__ == '__main__':
    my_func()

Run with the memory_profiler package:

pip install memory_profiler
python -m memory_profiler memory_example.py

Output example

Sampling Profilers

Instead of tracing every function call, sampling takes periodic snapshots.

Use case: You want a lightweight view of hotspots without slowing your app down too much.

Output example

Real-World Profilers

• Python: cProfile, PySpy, line-profiler

• JavaScript: Chrome DevTools Performance tab, Node.js built-in profiler

• Java: VisualVM, JProfiler

• Go: pprof

• C/C++: gprof, Valgrind

If your language has a runtime, it probably has a profiler.

What Developers Usually Look For

When developers run a profiler, they’re not scanning every number.

They’re hunting for patterns:

• Hotspots: “Where’s my code spending most of its time?”

• I/O Bottlenecks: “Is my app waiting on something external?”
  A slow SQL query, a network request to an API, or reading a giant file can all block performance.

• Memory Leaks: “Am I hoarding memory?”
  In languages with garbage collection (Python, JS, Java), this can creep in through forgotten references. In C/C++, leaks are even deadlier.

• Garbage Collection Pressure: “Is the runtime constantly cleaning up?”
  If the GC runs too often, performance tanks. Profilers show how much time is spent collecting trash vs. doing real work.

• Inefficient Loops/Recursion: “Did I accidentally build an algorithm that’s O(n²) instead of O(n)?”
  (Spoiler: probably yes, at least once in your career.)

• Expensive Library Calls: “Is this ‘helper function’ from a third-party library actually hiding a huge cost?”

When to Use a Profiler

• When your code runs too slow and you can’t tell why

• When you suspect a memory leak

• Before optimizing (so you don’t waste effort)

• After big changes, to catch regressions early

• During performance reviews or stress tests

A Simple Profiler Workflow

If you’ve never used a profile that’s fine!

Here’s a simple workflow just in case you feel like trying one:

1. Reproduce the problem 

   Run your code under normal conditions so the profiler captures the issue.

2. Start the profiler

3. Look for hotspots

   Focus on the areas that have issues in CPU or memory usage.

4. Ask why

   Is this function being called too often? Is it waiting on something external?

5. Fix one thing

   Optimize, restructure, or cache. Don’t fix everything at once.

6. Rerun the profiler

   Check if performance actually improved.

Optimizing performance is not always simple and the problems aren’t always obvious, but a profiler gives you the map.

It shows you where a slowdown is and it’s often in places you’d never expect.

So if you’re ever in a situation where your code feels slow, try a profiler!

Thanks to everyone who submitted!

grcc492, JunKaiPhang, AryanTheIndoDev, jmartinl, Wakorithegreat, NeoScripter, AspenTheRoyal, alfalconetti, SanjnaSukirti, and jsjasee.

Looks like graph like problems are difficult for you all 😏 

So let’s do another one!

Can You Exit the Maze?

You are given a 2D matrix representing a maze, where 0 is a walkable path and 1 is a wall.

You start at the top-left corner and you have to reach the bottom-right corner.

Write a function that returns true if a path exists.

You can only move up, down, left and right. You cannot move diagonally.

Examples

canExit([
  [0, 1, 1, 1, 1, 1, 1],
  [0, 0, 1, 1, 0, 1, 1],
  [1, 0, 0, 0, 0, 1, 1],
  [1, 1, 1, 1, 0, 0, 1],
  [1, 1, 1, 1, 1, 0, 0]
])
output = True

canExit([
  [0, 1, 1, 1, 1, 1, 1],
  [0, 0, 1, 0, 0, 1, 1],
  [1, 0, 0, 0, 0, 1, 1],
  [1, 1, 0, 1, 0, 0, 1],
  [1, 1, 0, 0, 1, 1, 1]
])
output = False
# This maze only has dead ends!

canExit([
  [0, 1, 1, 1, 1, 0, 0],
  [0, 0, 0, 0, 1, 0, 0],
  [1, 1, 1, 0, 0, 0, 0],
  [1, 1, 1, 1, 1, 1, 0],
  [1, 1, 1, 1, 1, 1, 1]
]) 
output = False

# Exit only one block away, but unreachable!

canExit([
  [0, 1, 1, 1, 1, 0, 0],
  [0, 0, 0, 0, 1, 0, 0],
  [1, 1, 1, 0, 0, 0, 0],
  [1, 0, 0, 0, 1, 1, 0],
  [1, 1, 1, 1, 1, 1, 0]
])
output = True

That’s all from me!

Have a great week, be safe, make good choices, and have fun coding.

If I made a mistake or you have any questions, feel free to comment below or reply to the email!

See you all next week.

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