login.py

def login():
    print('Welcome to the eHealth program, please sign in')

    with open ('users.csv') as csvfile:
        database = csv.DictReader(csvfile)
    loggedin = False
    while loggedin != True:
        Username = input('Fill in your username: ')
        Password = input('Fill in your password: ')
        for row in database:
            Username_File = row['username']
            Password_File = row['password']
            Function_File = row['function']
            if Username_File == Username and Password_File == Password and Function_File == 'patient':
                loggedin = True
                print('Succesfully logged in as a patient.')
                #patientmenu()  # we will add this later on
            elif Username_File == Username and Password_File == Password and Function_File == 'arts':
                loggedin = True
                print('Succesfully logged in as a doctor.')
                #artsmenu()     # we will add this later on
            elif Username_File != Username and Password_File == Password:
                #loggedin = False
                print('Failed to sign in, wrong username.')
            elif Username_File == Username and Password_File != Password:
                #loggedin = False
                print('Failed to sign in, wrong password.')
            elif Username_File != Username and Password_File != Password:
                #loggedin = False
                print('Failed to sign in, wrong username and password.')
            else:
                print('Error 404, Login Not Found')

# ---- Main ---- #
login()

For: http://stackoverflow.com/questions/34899153/python-username-and-password-login-while-and-for-loop