Use these answers when you hit a roadblock in a practice project or need to explain a concept clearly. Each course section gives you a place to start.
Python Full Stack
How do I isolate dependencies for a Python project?
Create a virtual environment with python -m venv .venv, activate it for your shell and install the project packages inside it. Record the dependencies so someone else can recreate the environment.
Why does Django say no such table?
Your application may be pointing at a database where its migrations have not run. Check the database settings and use python manage.py showmigrations to inspect which migrations are applied before running migrate.
Why does my Python app raise ModuleNotFoundError?
Check the import spelling and confirm that the interpreter running the app is the one where you installed the package. Using python -m pip show PACKAGE helps check that interpreter’s environment.
Java Full Stack
What is the difference between the JDK and the JVM?
The JVM runs Java bytecode. The JDK provides the tools to develop Java software, including the compiler and a runtime.
Why does my Spring Boot app say port 8080 is already in use?
Another process is listening on that port. Identify it before deciding whether to stop it, or run your application on a different port and update any frontend or test URLs that call it.
What does HTTP 400 mean in a Spring Boot API?
It means the server considers the request invalid. Compare the submitted JSON and its content type with the controller’s expected fields, and check the response for validation details.
Data Analytics
Why did my SQL join increase the row count?
A row appears once for each matching row on the other side. Check whether the join key is unique on either table before summing amounts across the result.
Why do totals change when I use a Power BI slicer?
A slicer changes the filter context for the visuals it affects. Check the field used by the slicer, its relationships and whether the measure deliberately removes a filter.
When should I use a pivot table in Excel?
Use a pivot table when you want to summarize rows by categories such as month and region. Check whether the value field is set to sum, count or another calculation before sharing the totals.
Data Science
What is a baseline model?
A baseline is a simple reference that tells you whether a more complex model adds value. For classification, one baseline always predicts the most common training label.
What is the difference between precision and recall?
Precision asks how many predicted positives were actually positive. Recall asks how many actual positives the model found. Pick a metric based on which kind of error costs more.
Why is my training score much higher than my test score?
The model may be overfitting, or the test data may differ from the training data. Compare the splits and baseline, then see whether a simpler model narrows the gap.
Cloud AWS and DevOps
What is the difference between an IAM user and an IAM role?
An IAM user is an identity that can have credentials. An IAM role is an identity that trusted users, services or workloads can assume to obtain temporary credentials.
What is the difference between a Docker image and a container?
An image contains the files and instructions needed to start a container. A container is an instance of that image that can be started, stopped or removed.
Why can’t I connect to my EC2 instance over SSH?
Check whether the instance is running, whether you are using the right username and key, and whether the network path and security group allow SSH from your IP.
Digital Marketing
What is click-through rate?
Click-through rate is clicks divided by impressions, expressed as a percentage. Ten clicks from 200 impressions gives a CTR of 5%.
What are UTM parameters used for?
UTM parameters label links with campaign details such as source, medium and campaign name. Consistent labels help group visits from different channels in analytics reports.
What is the difference between a lead and a form click?
A form click shows someone interacted with the form or its button. A lead requires a completed contact action under your definition, such as a successful enquiry submission.
New to these topics? Read the beginner Q&A guide for the fundamentals.
