10 Machine learning (scikit-learn, TensorFlow, Keras) Interview Questions and Answers for python engineers

flat art illustration of a python engineer

1. How did you first become interested in machine learning and data science?

My interest in machine learning and data science started during my undergraduate studies. I was studying computer science and I took a course on introductory machine learning. The ability of machines to learn from data and make predictions amazed me.

During the course, I worked on a project that involved predicting housing prices using linear regression. I collected data on various features such as the number of bedrooms, the area of the house, and the location, and used scikit-learn to build a model. The model predicted the prices with an accuracy of 85%, which was a great success for me.

After the course, I wanted to learn more about machine learning and started studying on my own. I read books, attended online courses, and practiced on Kaggle competitions. In one competition, I worked on a project that involved predicting customer churn for a telecom company. I used TensorFlow and Keras to build a neural network and achieved an accuracy of 90%, which was the second highest in the competition.

My passion for machine learning and data science kept growing, and I decided to pursue a graduate degree in the field. During my graduate studies, I worked on several research projects related to natural language processing and computer vision. One of the projects involved building a sentiment analysis model for customer reviews, which achieved state-of-the-art results in the benchmark dataset.

2. Tell me about a real-world data problem you've solved using machine learning.

During my time as a data scientist at XYZ Company, I was tasked with improving the accuracy of a fraud detection model for a financial services client.

  1. First, I conducted extensive data cleaning to remove any duplicates, outliers, or irrelevant data points.
  2. Then, I used scikit-learn to split the data into training and testing sets.
  3. Next, I used several supervised machine learning algorithms, including logistic regression, random forest, and gradient boosting, to train and test the model.
  4. After several iterations and fine-tuning, I found that the random forest algorithm had the highest accuracy, with a precision of 92% and a recall of 88%.
  5. I then used Keras to build a neural network model and achieved even higher accuracy, with a precision of 95% and a recall of 93%.
  6. To further validate the model, I conducted a blind test on new data and found that the model had an accuracy of 94%, confirming the robustness of the solution.
  7. The final model was integrated into the client's existing fraud detection system, resulting in a significant reduction in false positives and saving the company millions of dollars in fraudulent transactions.

This experience not only honed my technical skills in machine learning but also taught me the importance of effective data cleaning and feature selection in building accurate models for real-world applications.

3. Can you explain overfitting and underfitting in machine learning?

Overfitting and underfitting are two common problems in machine learning. Overfitting occurs when a model learns the details and noise in the training data to the extent that it negatively impacts the performance on new data. On the other hand, underfitting occurs when a model is too simple and cannot capture the underlying patterns in the data.

  1. Overfitting Example: Let's say we have a dataset of 100 images of cats and dogs, with a binary classification task to predict whether an image contains a cat or a dog. We train a deep neural network on this dataset and obtain a high accuracy of 95%. However, upon testing the model on a new dataset, we only achieve an accuracy of 70%. This is a clear sign of overfitting, where the model has learned the details and noise specific to the training set, but failed to generalize to new data.
  2. Underfitting Example: Continuing the previous example, let's say we have an extremely simple model that always predicts "dog" for every image. In this case, we would achieve an accuracy of 50%, which is no better than random guessing. This is an example of underfitting, where the model is too simple and cannot capture the underlying patterns in the data.

Both overfitting and underfitting can be addressed through various techniques such as regularization, cross-validation, and adjusting the complexity of the model. It is important to strike a balance between the model's ability to fit the training data and its ability to generalize to new data.

4. What's the difference between supervised and unsupervised learning? Could you give an example of each?

Supervised Learning

  1. Definition: Supervised learning is a machine learning method where the model learns from labeled data, meaning the input data has a corresponding output value.
  2. Example: A common example of supervised learning is classifying emails as spam or not spam. A dataset of emails is labeled as either spam or not spam, and the model learns from these labels to predict whether a new, unlabeled email is spam or not.
  3. Result: The result is a classification model that can accurately predict the class of new, unseen data. For example, the model can accurately predict whether a new email is spam or not based on its content and other features.

Unsupervised Learning

  1. Definition: Unsupervised learning is a machine learning method where the model learns from unlabeled data, meaning the input data does not have a corresponding output value.
  2. Example: A common example of unsupervised learning is clustering customer data to identify patterns or segments. A dataset of customer data, such as demographics and purchase history, is provided to the model. The model identifies similar patterns and groups the customers into clusters based on those patterns.
  3. Result: The result is a clustering model that can identify patterns or segments in the data. For example, the model may identify that customers who purchase a certain type of product are more likely to be of a certain age group and from a certain geographic location.

5. What experience do you have with scikit-learn? What are its primary strengths and limitations?

During my time at XYZ Corp, I worked extensively with scikit-learn on a project to build a predictive model for customer churn. I used a variety of machine learning algorithms available in scikit-learn, including logistic regression, decision trees, and random forests. After testing and comparing several models, we were able to achieve an accuracy rate of 90%, which was a significant improvement over our previous model.

In my opinion, one of the primary strengths of scikit-learn is its extensive library of machine learning algorithms, which can be easily implemented with just a few lines of code. This makes it an ideal tool for quickly prototyping and experimenting with different models. Additionally, scikit-learn has excellent documentation and user community, which makes it easy to learn even for users without a background in machine learning.

However, scikit-learn does have some limitations. One of the major ones is that it is not suitable for handling big data. As the size of the dataset grows, scikit-learn becomes increasingly slow and memory-intensive. In these cases, it may be necessary to switch to more specialized tools like Apache Spark or TensorFlow.

  1. In summary, my experience with scikit-learn has been very positive, and I believe it is an excellent tool for building and testing predictive models. Its primary strengths include a wide range of algorithms and excellent user community, while its limitations include difficulties with big data.

6. What experience do you have with TensorFlow? What are its primary strengths and limitations?

I have extensive experience working with TensorFlow, having used it in multiple projects. The primary strength of TensorFlow is its ability to handle large datasets and complex neural network models, making it ideal for deep learning applications.

In a recent project, I used TensorFlow to develop a deep learning model to classify images of cats and dogs with an accuracy of 96%. This involved training the model on a dataset of 10,000 images and fine-tuning the model using transfer learning.

However, one limitation of TensorFlow is its steep learning curve, particularly for beginners. Additionally, developing custom layers or models can be challenging, requiring a strong understanding of mathematical concepts and complex algorithms.

Despite these limitations, TensorFlow remains a powerful tool for deep learning and machine learning applications, and its versatility means it can be used in various industries, including healthcare, finance, and robotics.

7. What experience do you have with Keras? What are its primary strengths and limitations?

During my previous job as a data scientist at XYZ company, I used Keras extensively for developing multiple deep learning models. With Keras, I was able to quickly prototype and iterate on different models, which greatly reduced development time.

One of the primary strengths of Keras is its user-friendly interface. It provides a simple and intuitive API that allows for quick and easy model development. Keras also has great documentation and a large community, which make it easier to find solutions to common problems.

Another strength of Keras is its ability to run on top of different backends such as TensorFlow, Theano, and CNTK. This allows for more flexibility in choosing the backend that best suits the project requirements.

However, Keras also has some limitations. For instance, it is not as customizable as other deep learning frameworks like TensorFlow and PyTorch. In addition, Keras does not support distributed training out of the box, which can be a disadvantage when training large models.

To showcase my experience with Keras, I developed a deep learning model for image classification that achieved a test accuracy of 95%. The model used a Convolutional Neural Network architecture with multiple layers, which was implemented using Keras with a TensorFlow backend. The project involved data preprocessing, hyperparameter tuning, and cross-validation techniques.

  1. Used Keras extensively for developing multiple deep learning models
  2. Primary strengths:
    • User-friendly interface
    • Great documentation and large community
    • Ability to run on top of different backends
  3. Primary limitations:
    • Not as customizable as other deep learning frameworks
    • Does not support distributed training out of the box
  4. Developed a deep learning model for image classification that achieved a test accuracy of 95% using Keras with a TensorFlow backend

8. How do you determine which machine learning algorithm to use for a given problem? What factors do you consider?

When deciding which machine learning algorithm to use for a given problem, several factors should be taken into consideration:

  1. Type of problem: The type of problem we are trying to solve (classification, regression, clustering, etc.) will help us determine which algorithm is appropriate. For example, if we are dealing with a binary classification problem, then using logistic regression or a decision tree algorithm may be the best option.
  2. Data size: The size of the data we have can also influence which algorithm we choose. For large datasets, deep learning algorithms like TensorFlow or Keras may be more suitable, while for smaller datasets we may use simpler algorithms like scikit-learn's support vector machines.
  3. Data quality: The quality of the data can impact the choice of algorithm. For noisy data, we may choose more robust algorithms like decision trees or random forests, while for clean data simpler algorithms like linear regression may work just as well.
  4. Computational resources: The amount of computational resources we have available can also affect the algorithm we use. Deep learning algorithms like TensorFlow and Keras can require a lot of computational power and processing time, while simpler algorithms like logistic regression can be faster to run.
  5. Accuracy requirements: Finally, the accuracy requirements for a given problem can also influence the choice of algorithm. For example, if high accuracy is required, then using a more complex algorithm like a deep neural network may be necessary.

During a recent project, I was faced with the task of predicting customer churn for a telecom company. After reviewing the data and considering all of the factors mentioned above, I decided to use a random forest algorithm. The dataset was relatively small (around 100,000 records), and the data quality was good, so I didn't need to use a more complex algorithm like a neural network. The random forest algorithm was able to achieve an accuracy of 85%, which was sufficient for the project's requirements.

9. Tell me about a time when you spent a significant amount of time on a project without achieving your desired outcome. What did you learn from the experience?

During my time at XYZ Company, I was tasked with improving the conversion rate of our e-commerce website. I spent months researching and analyzing user behavior data, creating user personas, and implementing various A/B tests to optimize our website's layout and copy.

Despite all of my efforts, the conversion rate remained stagnant and I was not able to achieve the desired 5% increase. I felt disappointed and frustrated, but I knew that I had to learn from the experience and move forward.

After reflecting on the project, I realized that I had become too focused on the technical aspects of optimization and had overlooked some key factors that affected user experience. For example, I had not taken into account the psychological impact of the website's color scheme and overall design. Additionally, I had not appropriately tested some significant changes that I had made on the website but instead relied on my own assumption.

With this realization, I went back to the drawing board and created a new strategy. I conducted user testing with real customers to gain important feedback about the website's design and layout. I also collaborated with a visual designer colleague to rethink our website's color scheme and branding, which resulted in significant user engagement and customer satisfaction.

Through this experience, I learned to think more holistically about the user experience and consider various factors that may affect user behavior. It reminded me that optimization is not just about technical changes but also about the user’s perspective. Ultimately, as a team, we achieved a 7% increase in our conversion rate and improved our customer satisfaction ratings.

10. What industry applications or business problems have you solved using machine learning?

During my time as a data scientist at XYZ Corp, I worked on a project where we used machine learning to address a common issue in the e-commerce industry - shopping cart abandonment.

  1. First, we gathered data on customer behavior such as browsing time, products viewed, and past purchase history.
  2. Using scikit-learn, we built a predictive model to determine which customers were most likely to abandon their shopping cart.
  3. We then implemented a recommendation engine using TensorFlow to suggest personalized product recommendations to customers based on their browsing and purchase history.
  4. The result was a significant reduction in shopping cart abandonment rates of up to 40% in some cases, leading to an increase in sales revenue.

Furthermore, I also worked on a project in the healthcare industry where we used machine learning to predict patient readmissions.

  • We utilized Keras to create a deep learning model that takes into account patient demographics, medical history, and treatment plans to predict the likelihood of readmission within 30 days of hospital discharge.
  • With this model, we were able to identify patients who were at high risk of readmission and provide them with additional medical care and support to prevent readmission.
  • This resulted in a 25% reduction in readmission rates and improved patient outcomes.

Overall, these projects have demonstrated my capacity to use machine learning to solve complex problems and drive tangible results in various industries.


Congratulations! You have just gone through ten machine learning interview questions and answers that will help you excel in your interview. However, now it’s time to focus on your next step - applying for the job. Two important aspects of a job application are preparing a cover letter and a resume that stands out. Don’t forget to write an impressive cover letter by following our guide on writing a cover letter for python engineers. Similarly, get ready to present a compelling resume using our guide on writing a resume for python engineers. But where to apply for remote Python engineer jobs? Look no further than our remote Python engineer job board. Find your dream job and take the first step towards a successful career!

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