I made the code automatic and made it so it doesn't spam the console. It only sends a message in the console when it starts for the first time, and when a nitro code that works gets generated. Here are my changes, feel free to use, or ignore. The chances of getting a discord nitro out of this is low, but at least with how I updated the code it'll be faster.

I removed most of the print functions, that way the while loop doesn't spam the console lol, otherwise I would have kept them in.

import requests
import random
import string

while True:
  num = 10
  with open("Nitro Codes.txt", "w", encoding='utf-8') as file:

      for i in range(num):
          code = "".join(random.choices(
              string.ascii_uppercase + string.digits + string.ascii_lowercase,
              k = 16
          ))

          file.write(f"https://discord.gift/{code}\n")


  with open("Nitro Codes.txt") as file:
      for line in file.readlines():
          nitro = line.strip("\n")

          url = f"https://discordapp.com/api/v9/entitlements/gift-codes/{nitro}?with_application=false&with_subscription_plan=true"

          r = requests.get(url)

          if r.status_code == 200:
              print(f"\n\n Valid | {nitro}\n\n") #If the nitro code will be valid, it will print the code

Since the file ("Nitro Codes.txt") is full of "https://discordgift/{code}", in the following loop:

for line in file.readlines():
    nitro = line.strip("\n")

nitro is in the same format (https://...), so

url = f"https://discordapp.com/api/v9/entitlements/gift-codes/{nitro}?with_application=false&with_subscription_plan=true"

creates an url that looks very weird, that will throw a 404 error at any times.

There's another problem: rate limits Discord is hard limiting this endpoint, so it will blocks like 9/10 codes