Wells Fargo SE Interview: Python, Java & AI Behavioral Prep

Wells Fargo SE Interview: Python, Java & AI Behavioral Prep | DevMentor

So you've landed a Wells Fargo Software Engineer interview — congratulations. Now the real work begins. This role is a fascinating mix: Python as your primary language, some Java basics sprinkled in, and a set of behavioral questions that now include AI-related scenarios. That last part trips up a lot of candidates who aren't expecting it.

Let me walk you through exactly what to expect, how to prepare, and — most importantly — how to present yourself so the interviewer walks away thinking, "That person gets it."

What Wells Fargo Is Really Looking For#

Here's the thing most people miss: Wells Fargo isn't just hiring a coder. They're hiring someone who will work on financial systems where reliability, security, and ethical decision-making matter enormously. When I've seen candidates crash Wells Fargo-style interviews, it's usually because they optimized purely for algorithmic cleverness and ignored the "can I trust this person with sensitive financial data?" signal.

The interviewer is actually checking if you can:

Write clean, readable Python code (not just code that works)
Communicate your thought process clearly — especially under pressure
Demonstrate judgment when it comes to AI tools and ethics
Show that you've handled real workplace challenges with maturity

Keep that framing in mind for every answer you give.

Part 1: The Python Technical Screen#

What to Expect#

For a Python-primary role at Wells Fargo, expect questions around data manipulation, object-oriented design, and error handling. Financial systems love things like processing transactions, validating data pipelines, and handling edge cases gracefully. You won't just be asked to reverse a linked list — you'll be asked to do something that feels like a real fintech problem.

A Common Python Question You Should Nail#

Let's say they give you this:

"Write a function that processes a list of transactions and returns the total amount for each account, flagging any account with a negative balance."

A weak candidate just hacks together a loop. A strong candidate talks through their approach first, considers edge cases, and writes clean, readable code.

Here's how I'd want to see you write it:

python

from collections import defaultdict
from typing import List, Dict, Tuple
 
def process_transactions(
    transactions: List[Dict[str, float]]
) -> Tuple[Dict[str, float], List[str]]:
    """
    Processes a list of transaction dicts with keys 'account_id' and 'amount'.
    Returns total balance per account and a list of flagged account IDs
    with negative balances.
    """
    balances: Dict[str, float] = defaultdict(float)
 
    for txn in transactions:
        account_id = txn.get("account_id")
        amount = txn.get("amount",

What the interviewer is looking for here:

Type hints — shows you write production-quality Python
Docstring — shows you think about maintainability
Defensive coding (txn.get() instead of txn[]) — critical in financial systems
Meaningful variable names — not x, y, lst

A common trap is to immediately jump into writing code without asking clarifying questions. Before you type a single character, say: "I want to make sure I understand the input format. Are transactions always guaranteed to have an account_id? And should I handle duplicate transactions or is deduplication handled upstream?"

That question alone signals senior-level thinking.

Part 2: Java Basics — Don't Overcomplicate It#

If you're Python-primary, don't panic about Java. "Basics" means they want to see you're not completely lost if someone hands you a Java file. Focus on:

Understanding classes and objects
Basic OOP: inheritance, interfaces
Exception handling syntax
Collections (ArrayList, HashMap)

Here's a simple Java snippet you should be comfortable reading and explaining:

java

import java.util.HashMap;
import java.util.Map;
import java.util.ArrayList;
import java.util.List;
 
public class TransactionProcessor {
 
    public Map<String, Double> aggregateByAccount(List<Map<String, Object>> transactions) {
        Map<String, Double> balances = new HashMap<>();
 
        for (Map<String, Object> txn : transactions) {
            String accountId = (String) txn.

The interviewer is actually checking if you can read Java and reason about it, not write production Java from scratch. If they ask you about this, say: "In Python I'd use defaultdict here. In Java, map.merge() achieves the same result cleanly — it inserts if the key doesn't exist, or applies the merge function if it does."

Drawing that Python-to-Java parallel shows intellectual flexibility. Interviewers love that.

Red Flags to Avoid in the Java Section#

Saying "I don't really know Java" and stopping there — instead, say "I'm more fluent in Python, but let me walk through what I'd expect this to do..."
Confusing Java's static typing with Python's dynamic typing and not acknowledging the difference
Forgetting that Java uses null (not None) and failing to handle it

Part 3: The Behavioral Interview — STAR Format for Wells Fargo#

Okay, this is where I see the most wasted potential. Candidates spend 90% of their prep time on coding and 10% on behavioral — but at a company like Wells Fargo, the behavioral interview carries enormous weight. You're being evaluated for cultural fit, integrity, and how you handle pressure.

The STAR Framework (Use It Every Time)#

STAR stands for:

Situation: Set the scene briefly
Task: What were you responsible for?
Action: What did you specifically do? (Not "we")
Result: What was the measurable outcome?

Here's the mistake 80% of candidates make: they spend too much time on Situation and Task, then rush through Action and Result. Flip that. The interviewer already understands that projects have context. What they want to hear is YOUR judgment and YOUR impact.

Core Behavioral Questions for Wells Fargo SE Roles#

**1. "Tell me about a time you dealt with a production bug under pressure."

This is a Wells Fargo favorite because financial systems have zero tolerance for downtime.

Weak answer: "We had a bug and we fixed it."

Strong answer using STAR:

S: "During a quarterly reporting cycle at my previous role, our data pipeline started dropping transactions silently — no errors thrown, just missing records."
T: "I was on-call and responsible for diagnosing and resolving it within our 2-hour SLA."
A: "I started by isolating the issue — I added diagnostic logging to the ingestion function, ran it against a subset of data, and discovered a type coercion issue where certain float values were being cast to None during a schema validation step. I hot-patched the validation logic, ran regression tests on the last 72 hours of data, and coordinated with the DB team to backfill the missing records."
R: "We restored data integrity within 90 minutes, under our SLA. I then wrote a post-mortem and proposed adding a data volume assertion check to our pipeline — which was shipped the following sprint."

See how the Action is detailed and specific? That's what good STAR answers look like.

**2. "Describe a situation where you disagreed with a technical decision. How did you handle it?"

Wells Fargo values collaborative decision-making. They want to see you can push back professionally — not that you either fold immediately or go rogue.

How to talk through this: "I want to share a time I had a respectful technical disagreement that actually led to a better outcome for the team..."

Then: Describe the disagreement (S/T), explain how you gathered data or built a case (A), and highlight that you ultimately aligned with the team or influenced the decision constructively (R).

Part 4: The AI Behavioral Questions — This Is New and Tricky#

Wells Fargo, like most large financial institutions, is actively integrating AI tools while also being hyperaware of the regulatory and ethical risks. Expect questions like:

"Have you used AI tools in your development workflow? How do you validate their output?"
"How would you approach building an AI feature that impacts customer financial decisions?"
"Tell me about a time you identified a bias or risk in an automated system."

What the Interviewer Expects#

They're not expecting you to be an ML researcher. They ARE expecting you to demonstrate:

You use AI tools pragmatically (GitHub Copilot, ChatGPT for debugging, etc.) and understand their limitations
You think critically about AI outputs — you don't blindly trust them
You understand that in a regulated industry, explainability and auditability matter

Sample STAR Answer for an AI Question#

Question: "How have you used AI in your development work, and what guardrails did you put in place?"

S: "At my last role, we were exploring using an LLM to auto-generate SQL queries from natural language for an internal reporting tool."
T: "I was asked to prototype this and assess its feasibility for a customer-facing feature."
A: "I built a small proof-of-concept using the OpenAI API, but I deliberately added a human-in-the-loop review step before any query touched production data. I also created a test suite of 50 known query-result pairs to benchmark accuracy. When accuracy dropped below 90% for complex joins, I flagged it to the team and recommended we limit the feature to simple aggregation queries only — at least for the initial release."
R: "The scoped version launched successfully. We avoided a compliance risk that could have arisen from a hallucinated query running against customer financial data. The team appreciated the measured approach."

That answer shows technical judgment AND risk awareness — exactly what Wells Fargo wants.

Where Candidates Get Stuck#

Using "we" instead of "I": The interviewer is evaluating YOU. Say "I proposed," "I identified," "I implemented."
Vague results: "It went well" is not a result. "We reduced processing time by 40%" or "zero incidents in the 6 months following" IS a result.
Not preparing AI stories: Many candidates have used Copilot or ChatGPT but never thought to turn that into a story. Think now — when did you use AI, what did it get wrong, and how did you catch it?
Panicking on Java: If you go blank, say: "I'm more fluent in Python, but reasoning from first principles, I'd expect this to..." and keep going.
Ignoring Wells Fargo's values: Research their core values (integrity, diversity, inclusion) and subtly echo them. Say "I believe in transparent communication" not because it sounds nice, but because it's genuinely what they filter for.

How to Talk Through This in an Interview#

Here's example dialogue you can adapt:

Opening a coding problem:

"Before I start coding, let me clarify a few things. What's the expected size of the input? Should I optimize for time or readability first? Are there any constraints around the data types I should know about?"

Transitioning from approach to code:

"My initial approach would be to use a hash map to track balances in O(n) time. Let me code that up and we can discuss trade-offs after."

Handling a follow-up you didn't expect:

"That's a great question. I haven't thought about that specific edge case — let me reason through it out loud..."

Connecting a behavioral answer to Wells Fargo specifically:

"I think that experience is particularly relevant to a role at Wells Fargo, where the cost of data integrity issues is much higher than in other industries."

Follow-Up Questions to Prepare For#

Question	What They're Testing
"How would you scale this solution?"	Systems thinking beyond the immediate problem
"What would you do differently?"	Self-awareness and growth mindset
"How did your teammates respond?"	Collaboration and influence
"What if the AI model was wrong?"	Risk thinking and validation instincts
"How does this relate to financial compliance?"	Domain awareness

Key Takeaways#

Python: Write production-quality code — type hints, docstrings, defensive coding. Think fintech, not just algorithms.
Java: You don't need to be an expert. Show you can read it, reason about it, and map concepts from Python.
Behavioral STAR: Front-load your Action and Result. Use "I" not "we". Have 5-6 stories ready that can flex to different questions.
AI questions: Have a real story about using AI tools AND being skeptical of them. In a regulated industry, your judgment matters more than your enthusiasm.
Wells Fargo culture: Integrity, risk-awareness, and collaboration are the undercurrents of every question. Echo those values authentically.
Recovery: If you get stuck, say it out loud — "Let me think through this for a moment" — and keep reasoning. Silence is worse than a slow, thoughtful answer.

You've got this. Prep your stories now, practice saying them out loud (not just in your head), and walk in knowing that the interview is as much about how you think as what you know.