While loops in Python 3

Question

I'm having some problems with some code for a menu system. What I have so far isn't completed but I'm having a problem with it. It works fine with the account.leeman' but I can never get 'administrator' to work, and it always rolls back to the beginning. I've looked at the code for a while now but I can't figure out why this is and why it doesn't ever continue. The 'add' part of the code can be ignored as it isn't a problem yet, although if you can see any way in improving it, please let me know

So this is what I have:

usernames=["m.leeman","administrator"]
passwords=["pA55w0rd","password"]
while True:
 count=0
 add_or_enter=input("Would you like to Enter a username or Add a new one?: ").lower()
 if add_or_enter=="enter":
 username=input("Please enter username: ")
 while (count+1)!=(len(usernames)):
 #problem somewhere here
 if username==usernames[count]:
 print("Username accepted")
 password=input("Please enter password: ")
 if password==passwords[count]:
 print("Welcome "+str(username))
 print("Continue here")
 else:
 print("Incorrect password")
 else:
 count+=1
 if count==len(usernames):
 print("User does not exit")
 else:
 ()
 #should run again after this
 elif add_or_enter=="add":
 new_user=input("Enter a new username: ")
 if (new_user=="add") or (new_user==usernames[count]):
 print("Username unavailiable")
 else:
 count=+1
 if count==len(usernames)-1:
 usernames.append(new_user)
 new_password=input("Enter a password for this user: ")
 passwords.append(new_password)
 print("User "+new_user+" successfully created")

Any replies will be very helpful. Thanks.

• roganjosh: What is the desired behaviour?
• Kevin: Hypothetically, what happens if you do while count != len(usernames): instead?
• chickity china chinese chicken: Seems like there may be some hidden newlines in the user input from raw_input username and "m.leeman\n", At the line after you have indicated "#problem somewhere here", try if username.strip()==usernames[count].strip(): to clean the strings and strip-off the newlines. Worked when I tried it.
• Munir: A word of advice - use a dictionary with usernames as keys and passwords as values. It will be much easier to handle and won't require all this loops.

Answer 1

Lets take a look at this line of code:

while (count+1)!=(len(usernames)):

On the first loop, count is 0 so 0+1 != 2 and the loop executes. Their inputted name "administrator" won't match "m.leeman" so count is increased by one and the loop will execute again.

This time, count = 1. So count + 1 = 2, which happens to be the length of usernames. The loop doesn't execute and the admin account is not found.

The solution? Remove the + 1

while count != len(usernames):

Hope this helps

Answer 2

you never get to administrator because you are double incrementing count. you have count being incremented in the condition and then in the else statement when it doesn't = m.leeman so take out the count+=1 after the else statement.