Path parameter
- Python course
- Advanced
- Lesson 52/83
- 5 min
Learn path parameters with /items/{id}.
Path parameter
A placeholder of the form {name} in the path becomes a path parameter. The function parameter with the same name matches it; FastAPI extracts the value from the URL and passes it.
@app.get("/items/{item_id}")
def read_item(item_id: int):
return {"item_id": item_id}With the type int, FastAPI converts automatically. If the value does not match, a 422 response is returned. This is ideal for routes that take a resource id.
Type conversion
You can give path parameters types like int, str, float. FastAPI converts the string from the URL to this type; if it cannot, a 422 response is returned.
@app.get("/items/{item_id}")
def read_item(item_id: int):
# item_id is an int here
return {"item_id": item_id, "tipi": type(item_id).__name__}Without a type, the parameter is treated as str. Giving a type strengthens validation and documentation.
Practice GET route with a path parameter
Start with from fastapi import FastAPI and from fastapi.testclient import TestClient. Define app = FastAPI(). With @app.get("/items/{item_id}") define def read_item(item_id: int): returning {"item_id": item_id}. Create a client with client = TestClient(app). Print the response body with print(client.get("/items/5").text).
Starter code
# bring in FastAPI from fastapi
# bring in TestClient
# define app
# add a get function at '/items/{item_id}' (with item_id: int)
# create a client with TestClient, query '/items/5' and print the bodySample solution
from fastapi import FastAPI
from fastapi.testclient import TestClient
app = FastAPI()
@app.get("/items/{item_id}")
def read_item(item_id: int):
return {"item_id": item_id}
client = TestClient(app)
print(client.get("/items/5").text)Expected output
{"item_id":5}
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 How is item_id obtained in @app.get("/items/{item_id}")?
- Through the function parameter Correct answer
- Through a global variable
- From the query string
- By reading from a file
Explanation: item_id is obtained through the function parameter with the same name.
2 Complete the path parameter route
@app.get("/items/____")
def read_item(item_id: int):@app.get("/items/{item_id}")
def read_item(item_id: int):Explanation: {item_id} is the path parameter placeholder.
3 Match the path parameter concepts
| Term | Meaning |
|---|---|
{item_id} |
Is the placeholder |
item_id: int |
Is a type conversion |
422 |
Is a validation error |
/items/{id} |
Is a path template |