How do APIs work?

Posted by JackDrawsStuff@reddit | learnprogramming | View on Reddit | 20 comments

I’m slowly but surely learning how to program (python mainly, but I’m dabbling with web stuff too). One project I want to try is a little search field that searches for a term on eBay and returns a number of listings and averages their price or something similarly basic. From what I understand you would use an API to talk to a site like eBay and get it to return that information. What does that look like? How do you access or control a sites API? Thanks!

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20 Comments

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Capital_Rhubarb5524@reddit

I find this article very helpful. https://www.reddit.com/user/BlockByte_tech/comments/1b9jsa7/why_are_apis_needed/

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birdyfowrd@reddit

When a human being loads an ebay webpage, the browser is translating it into a bunch of GET requests to obtain resources like images etc. There are various HTTP verbs like GET, UPDATE, POST etc. The browser may also run scripts, for example executing scripts on a webpage to process how items are displayed. So how do you find what API endpoints you have access to? You can run a MITM proxy on the site like Fiddler to view exactly what requests are being sent. Then you can replicate those calls in your code. However, these days since it's not the 2000s anymore most sites have bot protection mechanisms. Cloudflare is the most popular one. For example, if you send too many requests in one go you might be flagged and if you try and load a page without having js enabled you might trigger the bot protection on the page and the endpoint may refuse to return information and you can also get your IP banned if they see too much suspicious activity on your end.

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JackDrawsStuff@reddit (OP)

How does a site tell the difference between a browser accessing its information and a program?

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Hypersion1980@reddit

API is just someone else function.

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football_programming@reddit

Literally trying to scrape data all damn day and can’t figure it out lmao

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Thresher_XG@reddit

In basic terms you send a request to a server and get back data. Look at eBay’s docs only way to see how to access their api

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ravenousld3341@reddit

Generally you don't "Control" an API. You ask it for information and use that information to perform other tasks. [Get Started | eBay Developers Program](https://developer.ebay.com/develop/get-started) This link should start pushing you in the correct direction. Normally the API documentation contains example code that covers basic queries. This document covers the buy api [Browse API resources | eBay Developers Program](https://developer.ebay.com/api-docs/buy/browse/resources/methods) These have references to what methods will return what information. You can use something like postman to try out these API calls and see what information is returned and in what format.

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Select-Young-5992@reddit

This is the answer to OPs question. OP, generally you need to create a developer account with whatever service you’re trying to communicate with. Once you do, you’ll get an api key along with documentation on all their endpoints

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Muhammad_C@reddit

**How do you access an API?** You’d have to make a request with the API endpoint for said API resource. *Note: JavaScript-wise, you can use the fetch() API* ***API Endpoint*** An API endpoint is a URL for the resource. Example: `/api/v1/ordered-items` **How do you control a sites API?** * Depending on where your API is deployed (ex: AWS) you can control the network traffic & which services/IPs can access it * When building the API you can design it so that when API requests are made the user has to pass in credentials to authenticate themselves **How do you control a sites API?** You won’t be the one controlling the API. The creators of the API will be the ones who control the API. All you’d be doing as a user is using the API and accessing the data that they allow you to have access to. **eBay** eBay-wise, there might already be an API available to obtain the info that you want. You’d have to search to verify this.

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JackDrawsStuff@reddit (OP)

Thanks for the info! Since some sites charge to use their APIs, how does that work? For example, I can simply search eBay and read how many listings there are - then manually average the listing prices with a calculator. But if I wanted to build a site that goes and gets that information, having to pay for the API could prevent that. How do sites gatekeep that info?

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Muhammad_C@reddit

Sites would give each user an API key which is basically like your password for accessing the API. The API service can track how many API requests you’re making in x period of time and charge you based on x requests.

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Klutzy_Stranger_9824@reddit

It’s a means of communication between 2 different sets of software for some kind of data. It is enabled by the one from which a resource is retrieved. You can relate this to how within one codebase you could write a function and call it somewhere else, however, in this case, it’s happening somewhere else probably within code written in a different language. API requests are in this way, language agnostic. You need a bunch of listings from eBay. So eBay would have enabled API endpoints that can be accessed publicly to return listings based on search terms. There would be documentation for this. There is another answer that talks more about how APIs work and look. It is mostly accessed through the network using the HTTPS protocol. I would suggest learning more about how this protocol works to get a deeper understanding.

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FordCEO@reddit

Can you explain how you would write logic in a web API backend? I have a chess game but I want to put the logic in the backend so, does that go in a controller? Or a model class? how is adding logic a different approach vs say calling an external api

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dzooni3@reddit

Long story short: You have a restaurant and it has 3 sections: 1. Kitchen - responsible for food preparation 2. A waiter - acts as the bridge connecting the cookers and the table-styling team. The order request is taken to the kitchen. 3. You (Visitor) - you order the waiter

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Hockinator@reddit

I know this is a little self promoty but I made a custom GPT that calls APIs for you. Good tool to get started, and it's GPT so you can just ask anytime what it's doing, what these HTTP verbs are, what JSON is, whatever. You can use it on free APIs around the internet or whatever you want; it knows the Star Wars API by default too so you can just try that https://chat.openai.com/g/g-QeNbSmirA-postman-for-pms

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ehr1c@reddit

Think of an API like a contract, that says for some defined input `x` you'll get back some defined output `y = f(x)` in return. In the case of a web API which is what you're talking about, publicly-available web APIs will post documentation somewhere. All you need to do is make (usually) HTTP requests to a particular URL defined in the documentation, which will either return the data you're after or perform some function you want to run on the server.

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username-out@reddit

With all the other comments describing web APIs it’s worth noting that APIs are not restricted to the web and http.

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math_rand_dude@reddit

https://petstore.swagger.io is a good example of how APIs work (swagger is a way to document APIs)

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OmenVi@reddit

It's generally a URL to the API, followed by the operation, and the parameters that you're looking for. example: [https://www.domain.com/api/v1/Operation?$parameter1="info"](https://www.domain.com/api/v1/Operation?$parameter1="info") The API would then reply with a block of JSON, usually, with the data requested, OR, if the operation is a POST/PATCH, will update the info. HOW you go about this is entirely up to you. I don't know Python, so I couldn't tell you much, there. I use PowerShell pretty regularly to do some stuff with our ERP, but I know many languages support this.

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