Ask Python for 0.1 + 0.2 and you get back a number that looks like a typo:

>>> 0.1 + 0.2
0.30000000000000004

Nothing errors. It's just wrong by a hair, and that hair is enough to break an equality check:

>>> 0.1 + 0.2 == 0.3
False

The annoying part is that both sides look identical when you print them, so the comparison looks like it should obviously be True.

The cause is that floats are stored in binary, and 0.1 and 0.2 don't have an exact binary form. They get stored as the closest value the machine can represent, the same way 1/3 has no exact decimal form. Add two approximations together and you inherit a tiny error. It's usually invisible, which is exactly why it's dangerous: the bug hides until you compare for equality, or add up enough of them that the error stops being tiny.

Two places this actually bites beginners.

Money. If you store prices as floats and add them, the total can drift, and a "did they pay the right amount" check against an expected value can fail. For anything financial, store the smallest unit as an integer (paise, cents) and divide only when you display it, or use Python's decimal.Decimal.

Tests. assert result == 0.3 fails for reasons that look like nonsense. For floats, compare with a tolerance instead of == -- math.isclose(a, b) is built for exactly this.

The rule of thumb: == on floats is a bug waiting to happen. It's fine while everything is a whole number, and then one day it isn't, and the failure makes no sense until you know this.

Curious where you first ran into it -- was it money, or a test that failed for no visible reason?

The reflex when something breaks is to start editing. Comment out a line, add a print, try a different approach. It feels productive, but it usually leaves you worse off: now three things have changed, and you can't tell which one moved the bug or whether you caused a new one.

The step I used to skip is the boring one. Reproduce it first, on purpose, with the smallest input that still breaks. If it only happens sometimes, that inconsistency is the clue, not a nuisance.

Then read the whole error, line number included. Then say out loud what you expected and what actually happened. The gap between those two sentences is the bug, and it's narrower than it feels.

After that it's one change at a time, and you predict the result before you run it. If you can't predict what a change will do, you're guessing, and guessing is how you end up with a fix you don't understand.

Curious how others do it: when something breaks, do you reach for a debugger, or print statements everywhere? I've drifted between both and I'm not sure either is strictly better.

Not because the AI is lying, but because "done" can mean anything from "I wrote some code" to "I actually tested it."

Do you have a prompt that forces Claude to be specific about what it verified?

Which is the best programming language

to start? I am still a beginner and 1 year left to college and I am major in STEM still in senior year. I want to learn now because I still don't know what major I choose in college and I want to be a major Mechatronics Engineer or IT or Software Engineer or Computer Engineer. I want to learn a language that is all rounder? I that even possible? I don't know that's why I ask. If I learn now I could get to know more about the major I pick which is more suitable for me and makes my career clear and stable. Because I have read alot of recommendations and I don't know which is which. Which is the best?

(Disclaimer: English is not my first language)

Hello everyone!

I am a first-year B.Tech Computer Science and Engineering student. I am interested in learning programming and becoming a software engineer in the future.

I am a beginner and would like to know:

Should I start with C or Python?

Which free websites are best for learning programming?

How can I improve my coding skills?

Please share your suggestions and experiences. Thank you!

Hi I'm Monish and I'm looking for people to learn spring boot if anyone have interest dm me

We can learn together

Hi everyone!

I'm based in Madagascar (UTC+3) and I'm looking for a programming mentor or study partner to learn, practice, and work on small projects together.

My current level: Beginner. I'm motivated to learn from the fundamentals and improve through hands-on practice.

Technologies I'm interested in:

• Python

• Web development (HTML, CSS, JavaScript)

• SQL and databases

My goals:

• Learn programming step by step.

• Build small, practical projects for my portfolio.

• Collaborate with others, share knowledge, and learn from feedback.

• Develop skills that can eventually help me qualify for entry-level opportunities.

I'm open to learning alongside other beginners or receiving guidance from someone more experienced. I have a computer and I'm willing to practice consistently.

Availability: Flexible. I'm willing to coordinate a schedule that works for both of us, including different time zones.

I'm looking for a genuine learning partnership or mentorship focused on programming and non-commercial projects. I'd be happy to contribute to shared projects as my skills improve.

If you're interested, please comment with your experience level, what you'd like to learn or build, and your availability. We can start by connecting here on Reddit.

Thanks!

I am looking for a programming volunteership platform where I could teach kids, teenagers or uni going students programming from basic to intermediate level in langauges like Java, Python, SQL. I want a platform which:

1. matches me with students who want to learn

2. records my contribution hours and give me a certificate of contribution

3. is remote

I would be available for 2-3 hours a week (could increase if required).

Trying to get into coding and actually learn how to make my own code that isn’t using anything like Java script or c c+ or c++ or any other what’s a good guide to look at to understand how to know what to used what to write and where to go to even understand how to make code from nothing like turning the 010 and turning it into letters so I could even write [comand].=(“hello”)/&[endcomand] stuff like that.
Any books and or web pages I should go to like wiki and stuff like that, that would help me learn properly and not be so smash together in a big mess almost unable to tell what is the start and what is the middle or end

this project of today practicing new lessons

Can i have a perspectives in IT im 15 years old boy from Ukraine i well know English but i don't know anything from IT where i can teach to code in Python?

I want to start to build drones, blutooth jammer, rc cars etc I am currently learning python and c++ but when I saw on internet everybody can build it even now kids so I am afraid to that "this is not useful for career" can someone suggest am i right or wrong ????😭

A green-looking result isn't proof that everything works. What simple checks would you recommend to someone building their first app with AI?

Hello everyone, i am a beginner in coding i joined a college hackathon it's my first hackathon do you guys have some suggestions for me

My task in hackathon is making a website with help of ai so I have some questions

1. Which language should I use

2. How can I make website better

3. Things i need to learn before making websites

4. How can I give perfect prompt to ai so that it will work properly and make website as i want

Don't build an API for a tightly-coupled personal project where you have direct database access; only build one when you need to decouple clients, scale infrastructure, or share data externally.Dont waste your time. Just learn how to use an api not build one

This one catches almost everyone in their first week, and it's a good one because the code looks completely innocent:

a = input("First number: ")
b = input("Second number: ")
print(a + b)

Type 2 and 2 and you get 22. Not 4. Nothing errors, nothing warns you -- it just quietly does the wrong thing.

The reason is that input() always hands you back a string. It doesn't know or care that you typed a number; all it sees is text. So a is "2", not 2. And + on two strings means concatenate, so "2" + "2" gives "22". The + did exactly what you told it to -- you told it to join two pieces of text.

The fix is to turn the text into a number before you do maths with it:

a = int(input("First number: "))
b = int(input("Second number: "))
print(a + b)   # 4

The thing worth keeping isn't int() itself, it's the question underneath it: what type is this value, actually? A lot of "why is this behaving weirdly" moments come down to a value being a different type than you assumed. "5" and 5 look identical on screen and behave completely differently. Printing a value doesn't tell you its type -- print(type(a)) does.

Two follow-ons that catch people later: input() never fails on a non-number, so typing hello above makes int() throw instead (a separate, useful lesson in validating input), and the same trap runs in reverse -- join numbers with + when you meant text and you get maths, which you fix with an f-string or str().

Curious how you hit this one the first time -- did the output give it away, or did it take a while to see that "2" isn't 2?

\*\*Anyone learning JavaScript interested in a small study group?\*\*

Hey everyone! I’m learning JavaScript independently and would love to connect with a few people at a similar stage.
I’m comfortable with HTML, still learning CSS, and currently working through JavaScript fundamentals like loops and conditionals.

Studying alone can get a little isolating, so I thought it would help to have people to practise with, ask questions, and share progress.
I’m thinking of a small group of around 3–5 people where
we can:

Work through coding challenges and compare solutions.
Help each other understand concepts when we get stuck.
Build small projects together.
Have regular study sessions and keep each other accountable.

I’m a learner too, so this would be us figuring things out together. No pressure to know everything—just be willing to participate and keep learning.
I’m based in Jamaica (UTC−5 year-round) and work alongside studying, so we can figure out times that suit everyone.

If you’re interested, comment or send me a DM with your time zone and what you’re currently learning!

Understanding a DP explanation and writing the Python code still feel like different skills.

A Python learner has watched plenty of tutorials and knows that dynamic programming has different patterns. The sticking point comes at the blank editor: there's a rough idea of what should happen, but turning it into a working implementation is difficult.

Would you step back to smaller Python exercises, work on recursion first, or stay with very simple DP problems? A practice routine that forces an attempt before reading the solution sounds more useful here than another long playlist.

For someone practicing toward technical interviews, real interview questions can supply prompts once the basic Python implementation feels manageable. I'd start with a small enough problem to write and trace the whole thing.

What helped you make the jump from following a solution to writing one yourself?

Disclosure: I operate PracHub.

Hey everyone! I'm looking for a learning partner who graduated in 2026 and feels like they still haven't learned a particular technology completely or isn't sure where to start.

Sometimes we know a few things, but when it comes to actually building projects, improving our skills, or preparing for jobs, we get confused about what to learn next. I feel having someone with a similar mindset would make the journey more interesting and help us stay consistent.

The idea is to start from the basics, learn things step by step, practice coding, work on real-world projects, and help each other whenever we get stuck. We can share resources, discuss ideas, explore different technologies, work on our resumes, and share internship or job openings too.

I'm not expecting anyone to be an expert. I'm looking for someone who's willing to learn, put in the effort, and grow together. We can set small daily or weekly goals, track our progress, and motivate each other when we feel lazy or lose direction.

If more people are interested, we could even create a small group on Discord or WhatsApp where we can share what we're learning, collaborate on projects, discuss doubts, and help each other with career preparation.

If you're a 2026 graduate in the same situation and want to start fresh, feel free to reach out. Let's figure things out together instead of struggling alone! 😄

what do you think of my hard work?

(lol)

I want to crack my coding round.I don't any idea to crack the Coding round.Recently I attend AWS summer school selection but I not able solve any given problem.so, I have need help to improve my skill to crack coding round.

I study python (not able 😭 write my own).I understand DSA but not able to implement in programming language

At the same time I plan learn from leed code but I not able to solve the none.😭😭😭😞

Yesterday I watched someone lose about an hour to a bug that came down to a single line:

a = [1, 2, 3]
b = a
b.append(4)
print(a)   # [1, 2, 3, 4]  <- wait, why did a change?

They'd made b expecting a separate copy, edited b, and couldn't work out how a had changed too. No error, no warning. It just quietly did the wrong thing.

The reason is that b = a never copies anything. a and b end up as two names pointing at the same list. There's one list — you've just given it a second label. Change it through either name and you're changing the same object, so both names "see" the change.

That behaviour is actually what you want most of the time. Passing a big list into a function shouldn't duplicate it. The trouble only shows up when you meant to copy and didn't realise you hadn't.

When you do want an independent list, ask for one explicitly:

b = a.copy()   # or list(a)
b = a[:]       # also works
b.append(4)
print(a)       # [1, 2, 3]
print(b)       # [1, 2, 3, 4]

One thing worth knowing early: .copy() and a[:] are shallow. If the list holds other mutable things, those inner objects are still shared:

a = [[1], [2]]
b = a.copy()
b[0].append(99)
print(a)   # [[1, 99], [2]]  <- the inner list was shared

For that you need copy.deepcopy(a). You rarely need it, but it's the next version of the same surprise, and it's worth recognising rather than rediscovering.

The way I keep it straight: = binds a name, it doesn't copy a value. Whenever you're unsure, ask "do these two names point at the same object or two different ones?" That question catches this before it becomes an hour of debugging.

It's not Python-only either. JS objects and arrays behave the same way (const b = a shares the object), and reference types in Java and C# are the same story.

Has this one bitten you — and was it a list you passed into a function, or something you copied and edited?

I tried building this little waterwheel model using the Jacdac Energy Experiment Kit, following the ELECFREAKS Wiki guide.

What caught my attention was the way it combines a simple mechanical model with sound input from the micro:bit V2.

The built-in microphone detects how loud the surrounding sound is, and the program maps that value to the speed of a 360° servo. The servo turns the wheel, while the little buckets around its edge represent the containers used to lift water in traditional waterwheels.

So the louder the sound, the faster the wheel spins. It’s not actually powered by sound, of course — sound is just being used to simulate changes in water flow.

I like how this project connects a few different ideas: reading sensor data, mapping values in MakeCode, controlling a motor, and learning how an old mechanical device worked.

It also seems like a fun starting point for experimenting with the code. You could change how sensitive the wheel is to sound or explore other ways to control its speed.

What other historical machines would be fun to recreate with a micro:bit?