client.py

import requests as req
import concurrent.futures as cf
import string
import random

WORKERS = 32
random_str = ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(128))

def worker():
    while True:
        _ = req.put(
            "http://127.0.0.1:9999/not_found_url",
            data=random_str,
            headers={
                "Content-Type": "application/json",
            })


if __name__ == "__main__":
    executor = cf.ThreadPoolExecutor(max_workers=WORKERS)

    fs = []
    for _ in range(WORKERS):
        fs.append(
            executor.submit(worker)
        )

    for f in cf.as_completed(fs):
        print (f.result())

server.py

from flask import Flask, request
app = Flask(__name__)

@app.route("/", methods=["PUT"])
def hello():
    _ = (request.data)
    return "Hello World!"


if __name__ == "__main__":
    app.run(host='127.0.0.1', port=9999, debug=False, threaded=True)

python2:
pip install flask requests futures