Python : How to check if input is not equal to any item in a 2d array?

user_13367914 0
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I was trying to check if the username entered is equal to the second index of item in the list, and I tried to use !=, but it still keeps letting the same username to be registered. What's the problem with the code ?

Registering username :

user_list = [['usr1','Daniel'],['usr2','Raymond'],['usr3','Emanuel']]

name = input("Please enter your name : ")
while True:
     if name == '':
          name = input("Please enter your name : ")
     else:
          for user in user_list:
               if name != user[1]:
                    break # break out for loop
          else:
               print("This username has been registered")
               name = input("Please try another username : ") 
               continue # continue the while loop
          break # break out while loop
print("Username registered as",name)

Editted:

The results of != and == seems to be different, the == works.

Login username :

user_list = [['std1','Daniel'],['std2','Raymond'],['std3','Emanuel']]

name = input("Please enter your name : ")
while True:
     if name == '':
          name = input("Please enter your name : ")
     else:
          for user in user_list:
               if name == user[1]:
                    break # break out for loop
          else:
               print("Unregistered username")
               name = input("Please try another username : ") 
               continue # continue the while loop
          break # break out while loop
print("Logged in as",name)
comparison-operators for-loop python
2 Answers

You're very close!
What you're trying to do: break out of the loop if there are any names in user_list that match the new name.
What it's currently doing: breaking out of the loop if there are any names in user_list that don't match the new name.
I.e., if you enter Daniel, since Daniel != Raymond, you will break early.

Instead, what you should do is break if the newly entered name is not present in a list of names:

user_list = [['usr1','Daniel'],['usr2','Raymond'],['usr3','Emanuel']]

name = input("Please enter your name : ")
while True:
    if name == '':
         name = input("Please enter your name : ")
    else:
        if name in [user[1] for user in user_list]:  # existing names list
            print("This username has been registered")
            name = input("Please try another username : ")
        else:
            break
print("Username registered as",name)
user_111217510

This code below will sort a lot of things out. In your code, even if we fix the indentation mistake with the else which should be moved into the for loop, the code won't work if we type Raymond. So I have provided an example which checks if the entered usr is in all the names in your user_list.

user_list = [['usr1','Daniel'],['usr2','Raymond'],['usr3','Emanuel']]

name = input("Please enter your name : ")
while True:
     if name == '':
          name = input("Please enter your name : ")
     else:
          for user in user_list:
               if name not in [lst[-1] for lst in user_list]:
                    break # break out for loop
          else:
               print("This username has been registered")
               name = input("Please try another username : ") 
               continue # continue the while loop
          break # break out while loop
print("Username registered as",name)
user_142222510
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