Flask Request & Response Objects

📥 request object

from flask import request
 
request.args.get("page")             # query string param, None if missing
request.args.get("page", 1)             # with default
request.args.get("page", type=int)         # with type conversion
request.args.getlist("tag")                   # repeated ?tag=x&tag=y
 
request.form.get("email")            # form (POST) data
 
request.get_json()                   # parsed JSON body (needs Content-Type: application/json)
 
request.method                       # "GET", "POST", etc.
request.headers.get("User-Agent")       # a header
request.cookies                          # cookies dict
request.files                               # uploaded files (see Flask File Uploads & Caching)
request.url / request.path                    # full URL / just the path
request.remote_addr                               # client IP

Always use .get(), never request.args["x"] — raises an error if missing.

get_json() returns None (not error) if Content-Type header is wrong, unless force=True.

📤 Response shapes

return "Hello"                        # 200, text/html
return "Nothing here", 404               # tuple → sets status code
return "Body", 404, {"X-Custom": "1"}       # tuple → status + headers
 
from flask import jsonify
return jsonify({"status": "ok"})              # JSON, correct Content-Type set automatically
return {"status": "ok"}                          # plain dict also auto-converts to JSON (Flask 1.1+)
 
from flask import Response
r = Response("body", status=200, mimetype="text/plain")
r.headers["X-Custom-Header"] = "value"
return r

Prefer jsonify() over manual json.dumps() — sets Content-Type correctly.

↩️ abort()

from flask import abort
abort(403)   # immediately stops execution, triggers error handler (see Flask Error Handling & Logging)

🧮 Status codes cheat table

Code	Meaning
200	OK
201	Created
301/302	Redirect
400	Bad Request
401	Unauthorized
403	Forbidden
404	Not Found
500	Internal Server Error

🔗 Next

Flask Forms & WTForms · Flask REST APIs & JSON