FastAPI app

Learn to create an app with FastAPI().

FastAPI app

FastAPI() creates an application object. It registers routes and dispatches requests to the matching function. With TestClient you test the app without running a server.

from fastapi import FastAPI
from fastapi.testclient import TestClient

app = FastAPI()

@app.get("/")
def root():
    return {"msg": "merhaba"}

client = TestClient(app)
print(client.get("/").text)

TestClient queries the app like an HTTP server; the body comes from resp.text, the status from resp.status_code.

Using TestClient

The TestClient(app) call returns a client object. On it you make requests with methods like get and post. You read the response body with resp.text.

client = TestClient(app)
resp = client.get("/")
print(resp.status_code)  # 200
print(resp.text)        # body

TestClient offers the same API as the requests library, so it feels familiar.

Exercise Test a FastAPI app

Start with from fastapi import FastAPI and from fastapi.testclient import TestClient. Define app = FastAPI(). With the @app.get("/") decorator define def root(): returning {"msg": "merhaba"}. Create a client with client = TestClient(app). Print the response body with print(client.get("/").text).

Show example solution

from fastapi import FastAPI
from fastapi.testclient import TestClient

app = FastAPI()

@app.get("/")
def root():
    return {"msg": "merhaba"}

client = TestClient(app)
print(client.get("/").text)

Test yourself

Which class tests a FastAPI app without a server?
- HTTPServer
- FastAPI
- BaseModel
- TestClient
Show answer

TestClient — TestClient queries the FastAPI app in memory.

Complete the TestClient call

from fastapi.testclient import TestClient

client = ____(app)

Show answer

from fastapi.testclient import TestClient

client = TestClient(app)

Match the FastAPI app concepts

FastAPI()

Creates the app
TestClient(app)

Gives a client
client.get(url)

Makes a request
resp.text

Gives body

Next lesson: @app.get

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