{"id":7,"date":"2024-11-02T14:43:03","date_gmt":"2024-11-02T19:43:03","guid":{"rendered":"https:\/\/douglasstarnes.dev\/?p=7"},"modified":"2024-11-02T14:51:54","modified_gmt":"2024-11-02T19:51:54","slug":"hello-fastapi","status":"publish","type":"post","link":"https:\/\/douglasstarnes.dev\/index.php\/2024\/11\/02\/hello-fastapi\/","title":{"rendered":"Hello FastAPI"},"content":{"rendered":"\n

Before using FastAPI you\u2019ll need to install a few Python packages. First is the fastapi<\/code> package. As the name suggests this contains the FastAPI framework modules. Next, you\u2019ll need uvicorn<\/code>. This is an ASGI server that will run the FastAPI application. Use pip<\/code> to install both.<\/p>\n\n\n\n

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$<\/span> <\/span>pip<\/span> <\/span>install<\/span> <\/span>fastapi<\/span> <\/span>uvicorn<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
In a new Python file (I\u2019ll use the name main.py<\/code>) import the FastAPI<\/code> class from the fastapi<\/code> module.<\/p>\n\n\n\n
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from<\/span> fastapi <\/span>import<\/span> FastAPI<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Next, create a new instance of the FastAPI<\/code> class.  I\u2019ll use the variable api<\/code>.<\/p>\n\n\n\n
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api <\/span>=<\/span> <\/span>FastAPI<\/span>()<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
To map URLs to handler functions, apply a decorator to a function that will handle requests to the URL.  Here the get<\/code> decorator maps the root URL to the hello_world<\/code> function.<\/p>\n\n\n\n
The hello_world<\/code> function simply returns a Python dictionary. Since FastAPI is designed for REST APIs, you don\u2019t need to render a template like you would with Django or Flask.  A REST API is likely going to respond with JSON data.  Conveniently, Python dictionaries and list transform nicely into JSON objects and arrays. FastAPI will transform Python types to JSON when possible.<\/p>\n\n\n\n
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@<\/span>api<\/span>.<\/span>get<\/span>(<\/span>"<\/span>\/<\/span>"<\/span>)<\/span><\/span>\ndef<\/span> <\/span>hello_world<\/span>():<\/span><\/span>\n  <\/span>return<\/span> <\/span>{<\/span>"<\/span>message<\/span>"<\/span>:<\/span> <\/span>"<\/span>Hello FastAPI<\/span>"<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Here is the complete code for the main.py<\/code> file:<\/p>\n\n\n\n
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from<\/span> fastapi <\/span>import<\/span> FastAPI<\/span><\/span>\n<\/span>\napi <\/span>=<\/span> <\/span>FastAPI<\/span>()<\/span><\/span>\n<\/span>\n@<\/span>api<\/span>.<\/span>get<\/span>(<\/span>"<\/span>\/<\/span>"<\/span>)<\/span><\/span>\ndef<\/span> <\/span>hello_world<\/span>():<\/span><\/span>\n  <\/span>return<\/span> <\/span>{<\/span>"<\/span>message<\/span>"<\/span>:<\/span> <\/span>"<\/span>Hello FastAPI<\/span>"<\/span>}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
To run the application invoke uvicorn<\/code> from the command line. It expects the name of the FastAPI instance which here is api<\/code> inside of the main<\/code> module. The \u2014reload<\/code> option will watch for changes in the code and restart if needed.<\/p>\n\n\n\n
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$<\/span> <\/span>uvicorn<\/span> <\/span>main:api<\/span> <\/span>--reload<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
As with all REST APIs, you could use a tool like Postman to test the application.  However, FastAPI includes a web interface that makes ad hoc testing much easier.  The interface can be found at \/docs<\/code>.<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
To interact with an endpoint expand an item.<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
Click the Try it out<\/strong> button to configure an HTTP request.  There are no options for this endpoint so click the blue Execute<\/strong> button. <\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
Scroll down a little and inspect the response.  As expected, the body of the response includes the JSON data returned by the hello_world<\/code> function.<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
That’s how easy it is to get started!<\/p>\n\n\n\n
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