Here is a list of popular examples.

1. Netflix: If you ever wanted evidence of a company that kept pace with digital change, Netflix is the one! While Netflix used to rent DVDs by post, they quickly jumped on the digital bandwagon and expanded to become one of the most popular streaming services in the world. Developers at Netflix explain that they use Python throughout “the full content lifecycle.” In short, this means that Python sits at the base of many Netflix applications from their security tools and recommendation engine, to their in-house content distribution network, Open Connect (which delivers streaming content to its end users). Now you know!
2. Reddit: The go-to forum for everything from news to bleeding-edge social commentary, Reddit has long been a staple of the world’s internet diet. Whenever you send a request via your browser to Reddit, the web server (Reddit) uses Python to translate your request. It then sends back the necessary HTML, which is what you see in your browser.
3. Spotify: Spotify makes heavy use of Python on its web backend, which comprises many interconnected services. According to the company, around 80% of these are coded using Python. Spotify also has a proprietary Python data analytics package called Luigi. Designed to quickly prototype complex data jobs, Luigi powers Spotify’s Radio and Discover features, as well as recommendations for people you might want to follow.
4. Dropbox: First launched in 2008, the file hosting service Dropbox was doing cloud storage. Today it remains at the cutting edge of the sector and much of its success is down to Python. Dropbox has used Python since its inception, both server-side and on the client end. The language’s cross-platform support and readability led Dropbox to adopt the language since these allowed them to implement, test and deploy new product features at speed. The company is also a firm believer in open-source. They regularly share their innovations with the wider world–something we like to see! The company is so focused on Python that, from 2012 to 2019, they even employed Guido van Rossum, Python’s creator.
5. Quora: Probably the internet’s most famous Q&A site (at least since Yahoo Answers departed—RIP) Quora is best known for its compelling questions and occasionally dubious responses. Nevertheless, it’s hugely well-known and is another site that makes heavy use of Python. Being such a dynamic site, Python has allowed Quora to build and test new functionality with fewer lines of code, streamlining their new feature development. In terms of their exact tech stack, Quora uses numerous Python libraries on its backend, including Tornado and PyPy, amongst others.
6. Uber: Like Quora, they tend to use Tornado at Uber. Python accounts for about 35% of their tech stack and much of its backend functionality relies heavily on it. This includes data analytics features for predicting supply and demand, user surges and arrival times—highly mathematical functions that Python is ideally suited to.
7. Amazon: In particular, Amazon engineers have produced Python machine learning algorithms that interact with the company’s Hadoop data storage system. This mighty analytics stack powers Amazon’s famed recommendation engine that encourages us to purchase new products. Analyzing user search and purchase habits, Python helps Amazon recommend even more stuff for us to buy!
8. Pinterest: The virtual pinboard and social bookmarking site Pinterest was initially built using Python, because that’s what languages its developers knew best. It’s since taken a more pragmatic approach, with former Pinterest Chief Technology Officer, Vanja Josifovski, explaining that Pinterest uses many programming languages depending on the use case. However, the site’s continued reliance on machine learning strongly suggests that Python remains a core part of their tech stack. 
9. Lyft: Also like Uber, Python is a core language at the company. According to their Principal Tech Lead, Roy Williams:     “It’s not uncommon for us to have services configured by Salt (written in Python) while running a web server with Flask, serving data with scikit-learn, and manipulating with Pandas… this is pretty common for us.”
10. Google: Today, Python is an “official language” at Google and has many continued applications across the organization, from system building and administration to code evaluation. Of course, as the need for data analytics becomes increasingly important in big tech, Python is also used in many of Google’s cutting-edge machine learning and AI projects.
11. YouTube: YouTube functionality including view video, administrator video, data access, and website control templates are just a few ways in which Python powers the site. 
12. Facebook (Meta): Python plays no small part, accounting for at least 21 percent of their codebase, mostly in the area of production engineering. Oh, and remember that Tornado web framework we mentioned (used by Quora and Uber)?
13. Instagram: Instagram’s original backend was built on a Django framework—still used to this day. And since Meta (formerly Facebook) bought Instagram, the integration between the two platforms has grown increasingly complex. APIs, search mechanisms, and other functionality are all coded in Python.
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