Check whether a value is in a list
You will often want to check if a certain value appears in a list, e.g. during a registration process to check whether the username already exists. This can be done using the in keyword:
names = ['Maria', 'Lucy', 'Angelina', 'Tanya'] new_name = 'Tanya' if new_name in names: print('The name already exists. Please choose another one.')
In the example above we’ve created a list called names with four items in it. We’ve then assigned a value of Tanya to the variable new_name. Since the value of Tanya exists in the names lists, the message was displayed, informing the user that she needs to choose a new username.