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Building Machine Learning Powered Applications

by Emmanuel Ameisen

The book of the week from 22 Nov 2021 to 26 Nov 2021

Learn the skills necessary to design, build, and deploy applications powered by machine learning (ML). Through the course of this hands-on book, you’ll build an example ML-driven application from initial idea to deployed product. Data scientists, software engineers, and product managers — including experienced practitioners and novices alike — will learn the tools, best practices, and challenges involved in building a real-world ML application step by step.

Questions and Answers

Álvaro Budría

Hi Emmanuel Ameisen, I’m a DS intern just one week into my internship. For novices like me, what are the crucial basic good practices, skills and ways of approaching the role that will make someone like me stand out?

Emmanuel Ameisen

That really depends on your team, company and the goal of the internship! More generally when onboarding to a new company, here are a few things I would always recommend doing:

  • Ask a lot of questions, especially at the start. Ask not only about subjects of interest, but meta-questions like “how can I find documentation by myself?” for example
  • Setup introductory chats with many folks on the team (I would aim for at least one chat a day for the first few weeks) to get to know them. In that process, ask about their priorities and goals. This will let you know what matters to different parts of the org, and angle your work to match.
  • Ask your manager and leaders what they think are the success and failure criteria ahead of time. Than, regularly check in to see whether you and them are in agreement on how everything is going
    Last but not least: in an internship, you are also evaluating the company as a potential place to work. Don’t forget to take the time to explore and decide whether this would be the right full-time role for you.
Álvaro Budría

You give an angle to this question that I didn’t think much about. I’ll be applying all these tips. thanks!

Nikhil Shrestha

Hello Emmanuel Ameisen
Thank you for writing this book.
As we usually talk a lot about statistics and learn too many concepts, also on the other hand we come across senior lecturers n experts etc who also claim that you in real world you don’t use the theory but you use some tricks or things in practical way.
To give small example: when we learn precision recall we find different tricks like Precision = Positive. The proportion of TP from all Positive labels
But when solving in competition or real time we go vertical for Precision and Horizontal for recall

  • My question is how does things actually work in real life ?
  • How and when is statistics or other theoretical topics actually used in real time ?
    Like I learnt from many instructors and webinars that they usually use practical statistics.
  • But what does practical stats actually mean ?
Emmanuel Ameisen

Right, the body of theoretical knowledge that is taught at school is often much larger than what you will need in an applied role. This doesn’t mean it isn’t useful to learn all these concepts, but it is good to be aware of the practical realities of the job.
For statistics specifically, I’d say it depends on your role. Some companies hire statisticians which may use every tool in their arsenal. For Data Scientists and ML Engineers, you’ll most commonly use stats to:

  • Understand model performance metrics, such as FPR/TPR, ROC curves, Brier scores, NDCG, etc
  • Design and interpret results of applied experiments such as A/B test. That includes understanding confidence intervals, statistical significance, MDEs, etc.
  • Understand model loss functions such as cross entropy loss and their impact on model training
Nikhil Shrestha

Thank you for the swift reply and yes I totally agree that theory is as important as knowing practicality. 🙂

Dustin Coates

Emmanuel Ameisen no question here, but a thank you. As a PM (“former” dev), your book was immensely valuable. Almost instantly, our team put into place the “do it manually first” rule in a way that we hadn’t before, and if that was the only thing we got out of it, it would have been useful enough, but I got much more. I’ve recommended your book to many others at my company.

Emmanuel Ameisen

I’m glad the book was useful and applicable to you and your team. It’s been amazing to hear which parts resonated with folks at different companies and roles. Thanks for the kind words and for recommending it to others! If you haven’t yet feel free to leave a review on Amazon if you have the time to let other PMs know to check it out, it really helps.


I agree 💯 Thank you for writing a great book on this topics and being here with us. One of my colleague loves your book and highly recommended it to all of us in the team. It was a huge help for him.


Hi Emmanuel Ameisen,
How do you validate an DS idea to full blown product? Is doing a quick PoC and then followed by agile methodology to build incrementally and deploy work or do you suggest anything else from your experience?

Emmanuel Ameisen

Love this question. One thing I try to focus a lot on in the book and in real life is making iteration cycles as short as possible. When validating an idea, you’re often trying to do a couple things at once:

  • Determine whether the product idea is useful before investing a lot of effort. For this, I recommend finding either a rule/heuristic or using humans to build a first version. Even if the performance isn’t close to what you think you can reach with ML, that will help you decide whether you need to work on this problem at all. Oftentimes at this point you will find a fundamental flaw in your product idea and rethink it
  • Figure out whether you need ML at all. ML is great, but it has very high maintenance burden. Few models are ever “set it and forget it” (see googles paper about ML being the high interest credit card of technical debt). This is a different problem, but the advice above applies to it pretty directly
  • Figure out whether ML can solve it. It may be the case that this is outside of the realm of what is doable today (“use ML to build a chatbot that can automate all of the work of a medical doctor” would be an example of something out of reach). For this, I recommend starting by carefully defining the inputs and outputs of your ML system (where is it going to live in your app? What information will it have access to? What kind of prediction will it make? How long will it have to make this prediction?). Once you have that, define what performance level will be your bar to ship this model. Base this on business outcomes! If you are building a recommencer system for a YouTube like service, you may for example decide that you’d only use a model that recommends at least one useful video to a user 80% of the time it displays recommendations. If the model will be used in a modal that shows three recommended videos, that means your top3 recall should be 80%.
    Once you have those, you can start your iteration loop of model building and evaluating. Of course you may learn more as you go along and fine tune these goals, but doing the work ahead of time will save months of time wasted in dead ends

How do you handle “pivots” in product development? For example: You start building your product around a particular framework later realise that there is a new superior framework out there. Do you have any steps which you follow to avoid these “pivots” in the future?

Emmanuel Ameisen

That’s a challenging one, and slightly outside the scope of my expertise. I’ll say that my experience is that pivots and refactors are always more costly than expected, so I generally require a strong motivation to buy in to one. Again, a bias for simplicity can help here as it makes swapping out any piece of your pipeline easier. It’s hard to say much more without a more specific situation


Thank you Emmanuel for all of your elaborate answers 🙂

Nikhil Shrestha

Hello Emmanuel Ameisen again
We hear this a lot, if you want to get into the industry you must make projects on real life situations solving real life problem
I want to know how we approach towards solving one. Are there some pointers which you could tell in terms beginning a project, challenges and some tips to tackle them.

Emmanuel Ameisen

Practical experience is very worthwhile, so working on a project is valuable. My only guideline for picking a project is to pick something applicable and useful, and get your hands dirty. In my experience the main value of a side project for recruiting folks that are early in their career is to show that they can be productive. Often times I hear students get hung up on how much ml or rl or computer vision their project contains. As long as you can show that you know the required theory, it actually doesn’t need to be part of an applied project. I would consider them separate and chose a project by finding a use case you like, not shoe horning an ML application to it

Nikhil Shrestha

Thank you for the insights and I will use these in practical from now on.🙏🙂

Nikhil Shrestha

Also we study significance level and confidence level in theory class
As I learnt from some webinars and tutorials. Real world situation they are used extensively, before every project SL and CL are decided and using them you decide if model is generalized or not and also model evaluation.
E.g. criteria could be train-score < test-score AND test-score > CL

  • My question is how far is this true. ?
  • If it is true then what happens to the results ?
    As I tried this technique in NLP and other ML data (toy data). I had to reduce my training accuracy to achieve this criteria.
  • So 90-99 % accuracies are myths 🙆
Emmanuel Ameisen

In my experience, confidence interval are more often used for superiority and non inferiority tests (is this model better than that one) both offline and online (A/B test).

Nikhil Shrestha

Thank you
Totally understood and makes sense

Álvaro Budría

Nikhil Shrestha what do CL and SL mean?

Nikhil Shrestha

SL is significance level and CL is confidence level.

Tim Becker

Hi Emmanuel Ameisen, thanks for this really interesting book!

Tim Becker
  • I was wondering which tech stack you are discussing in the book?
Emmanuel Ameisen

The book mostly uses the Python data science stack

Tim Becker
  • Which deployment options do you cover in the book?
Emmanuel Ameisen

The book doesn’t focus too much on deployment infra. It discusses trade offs at a high level though, like synchronous and batch server side approaches vs edge deployments. If you want to learn about that specifically though, you’ll probably want to check out more specialized books

Tim Becker
  • What is in your experience the most difficult part when building a ML powered application?
Emmanuel Ameisen

Understanding the user need and trade offs well enough to chose the correct technical approach. Being able to tell when the current approach is a dead end

Tim Becker
  • What are the most common pitfalls during the process of building ML applications? And how can we avoid these?
Emmanuel Ameisen

Starting from the ML and deriving the application from it (“it would be cool to ship a sentence model, we could use it to autocomplete searches on our clothing website”) vs the opposite (“users often miss relevant categories, so we should build a classifier based on search queries that suggests relevant categories to browse”)

Tim Becker

thank you for answering my questions 🙂


Hello Emmanuel, thank you for doing the QnA!
How do we measure the outcome of the model in test after measuring the output during train/validation phase?
What are the common indications to look for when the model does not do well in the production/test phase even when the outputs showed the model was doing well in validation phase?

Emmanuel Ameisen

Regressions happen all the time between your validation set and production. They are commonly caused by mismatches in data generation, either on the filtering side (you trained on an unrepresentative distribution of samples) or the feature computation side (the way you compute some feature is different online/offline). The best way I’ve found to detect those mismatches is to rely on a shadow infrastructure. Shadow means that in production you send a copy of the request you send to the prod model to your candidate model, and log its output. Because you don’t action the prediction in any way, it is a safe approach that gives you information about production performance.


Shadow infra is something new to me and interesting, will read about it! Thank you


Hi Emmanuel, thanks for doing this and for the insightful answers you have provided this far. Sounds like a great book!
What would you say is the minimal realistic practical size for a team to take a new project from prototype to production?

Emmanuel Ameisen

Depends on the scale of the project and company! For internal tools, or at companies with strong infrastructure, a single IC can ship a model to prod. For companies that are smaller, or projects that are more complex, teams can get arbitrarily large. Think of the number of software, hardware, data and ML engineers are required to ship Tesla self driving, or OpenAI GPT-3

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