What is the role and purpose of query parameters in request processing in frameworks like Django, FastAPI, and similar systems?

Query parameters are part of the URL that comes after the question mark (?) and are used to pass additional information to the server when processing HTTP requests. In frameworks like Django, FastAPI, and similar, they allow the client to pass filters, sorting parameters, pagination, and other data without changing the main path.

For example, in FastAPI, query parameters can be received as function arguments:

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/")
async def read_items(skip: int = 0, limit: int = 10):
    return {"skip": skip, "limit": limit}

Here, skip and limit are query parameters that the client can specify in the URL: /items/?skip=5&limit=20.

In Django, query parameters are accessible through the request.GET object, for example:

def my_view(request):
    page = request.GET.get('page', '1')
    return HttpResponse(f"Page: {page}")

Thus, query parameters allow flexible management of request behavior without changing the route and are used to pass optional data.