Common round types: Tech screen → Code review → System design → Algorithms → Behavioural. Often 45–60 min each.
Ask your recruiter: how many rounds, who you'll meet, remote or onsite, which languages are allowed. Most rounds leave time for your questions.
Typical format: remote, one engineer. Part 1: talk through your CV. Part 2: live coding on a shared online editor, explaining your decisions as you go.
Language: if you can choose, use the one you're fastest in (here: Python 3).
⏱ Rough plan
📄 CV discussion: how to prep
Pick 2–3 projects
One line each: problem, your part, result.
Know your choices
Be ready for "why X, not Y?"
Numbers
Scale, cost, time saved. Only real ones.
🗣 Saying decisions out loud
"I'll use a dict here so lookup is O(1)."
"I'm choosing clarity first; I'll optimise if we have time."
Practise with the problems in the ✏️ Algorithms tab.
Typical format: remote, in an editor such as VS Code. Read the code, fix bugs, suggest functional and non-functional improvements, discuss best practice.
🔍 How to run the review (tap a phase)
📄 The module: buggy_bank.py
It runs fine. The bugs are logic bugs. Download for VS Code, then run python3 buggy_bank.py.
🐞 11 planted issues
Try first. Then hint. Then answer.
✅ What to look for
🐍 Python idioms to suggest
@dataclass(frozen=True)
For values like Money and Posting.
Type hints + mypy
Catch float vs Decimal mix-ups before running.
Enum
For entry kinds, in place of strings like "deposit".
Pass in the store and the clock, so tests can swap them.
decimal.localcontext()
Set precision and rounding in one place.
zoneinfo
ZoneInfo("Europe/London") for business dates.
Per-account locks
A lock for each account, taken in id order.
🗣 Phrases that sound senior
"Let me first say what this code is for, then go top-down."
"This is a correctness bug. That one is style. I'd fix the first today."
"In a bank, I'd want this to be a ledger entry, not a balance edit."
"I'd add a test that fails first, then fix it."
Typical format: interactive scenario. The interviewers often outline the topic areas. Focus: your design choices and knowledge of specific technologies.
Rule #1: follow their scope. They outline the topics. Use the timeline below as a fallback, and ask "Which area would you like to go deep on?"
⏱ How to run the 60 minutes
For any vendor platform: don't guess API names. Say "I'd check the docs."
Typical format: a standard algorithm question, solved together, with you leading. Often on a whiteboard, any language.
🎤 Lead the session: what to say
Tap each phase. You drive. They are your teammates.
Typical format (behavioural): often onsite. Common areas: processes and systems you've used, working with clients and stakeholders, explaining technical ideas, and motivation.
⭐ How STAR works
SSituation: where, when, what was wrong. 1–2 lines.TTask: what you had to achieve.AAction: what you did. Most of the time goes here.RResult: outcome, with a number if you have one. What you learned.
Aim for about 2 minutes per story.
📝 Blank template
S[fill in]T[fill in]A[fill in]R[fill in]
🗺 Common behavioural areas → prepare a story for each
Processes & systems
CI, code review, testing, on-call, releases you have run.
Working with & managing clients
A hard stakeholder, a changed scope, a missed deadline.
Communicating technical ideas
Explaining a system to a non-engineer.
Motivation
Why this company, why this role, why now.
💡 Explaining tech simply
🎯 "Why this company / why this role"
Why the company
Link a real problem you have seen to what they build.
Why this role
Match what you enjoy to what the role does day to day.