newbie python - adding 'cilent' into the txt file

Question

I'm working on a registration in my school project, and one part of it is about registartion. I have to input client in form of

1. username
2. password
3. name
4. lastname
5. role

so he can be registered and appended into the txt file,

but i also have to make "username" be the unique in file (because I will have the other cilents too) and "password" to be longer than 6 characters and to possess at least one number.

Btw role means that he is a buyer. The bolded part I didn't do and I need a help if possible. thanks

def reg()
  f = open("svi.txt","a")

  username = input("Username: ")
  password = input("Password: ")
  name = input("Name of a client: ")
  lastname = input("Lastname of a client: ")
  print()
  print("Successful registration! ")
  print()

  cilent = username + "|" + password + "|" + name + "|" + lastname + "|" + "buyer"

  print(cilent,file = f)
  f.close()

Answer 1

You need to add some file parsing and logic in order to accomplish this. Your jobs are to:

1: Search the existing file to see if the username exists already. With the formatting as you've given it, you need to search each line up to the first '|' and see if the new user is uniquely named:

name_is_unique = True
for line in f:
   line_pieces = line.split("|")
   test_username = line_pieces[0]
   if test_username == username:
      name_is_unique = False
      print("Username already exists")
      break

2: See if password meets criteria:

numbers=["0","1","2","3","4","5","6","7","8","9"]
password_contains_number = any(x in password for x in numbers)
password_is_long_enough = len(password) > 6

3: Write the new line only if the username is unique AND the password meets your criteria:

if name_is_unique and password_contains_number and password_is_long_enough:
   print(cilent,file = f)

Edit: You may also have to open it in reading and writing mode, something like "a+" instead of "a".