Testing user input against a list in python

Question

I need to test if the user input is the same as an element of a list, right now I'm doing this:

cars = ("red", "yellow", "blue")
guess = str(input())
if guess == cars[1] or guess == cars[2]:
 print("success!")

But I'm working with bigger lists and my if statement is growing a lot with all those checks, is there a way to reference multiple indexes something like:

if guess == cars[1] or cars[2]

or

if guess == cars[1,2,3]

Reading the lists docs I saw that it's impossible to reference more than one index like, I tried above and of course that sends a syntax error.

• RichieHindle: Is it intentional that you're not looking at cars[0]? Lists are indexed from zero, so your three cars are cars[0], cars[1] and cars[2].
• Ant: i really hope you're using python 3.x...otherwise use raw_input instead of input and print 'succes!', without brackets
• Guillermo Siliceo Trueba: Yeah i'm aware of the 0 index in list thanks, And yes it is python 3.1

Answer 1

The simplest way is:

if guess in cars:
 ...

but if your list was huge, that would be slow. You should then store your list of cars in a set:

cars_set = set(cars)
....
if guess in cars_set:
 ...

Checking whether something is present is a set is much quicker than checking whether it's in a list (but this only becomes an issue when you have many many items, and you're doing the check several times.)

(Edit: I'm assuming that the omission of cars[0] from the code in the question is an accident. If it isn't, then use cars[1:] instead of cars.)

• sepp2k: I think you misunderstood the question. In the first example his code would not print success if guess is "red", but your code would.
• Daenyth: Something to note here is that set construction, while efficient, may be a point of overhead if you're only checking the list once.
• sepp2k: On the other hand, maybe I misunderstood and he simply made a mistake in his example code...
• Guillermo Siliceo Trueba: Thanks guys, yeah it was a mistake, but i'll keep that in mind, in, was what i needed :)

Answer 2

Use guess in cars to test if guess is equal to an element in cars:

cars = ("red","yellow","blue")
guess = str(input())
if guess in cars:
 print ("success!")

Answer 3

Use in:

if guess in cars:
 print( 'success!' )

See also the possible operations on sequence type as documented in the official documentation.

Answer 4

@Sean Hobbs: First you'd have to assign a value to the variable index.

index = 0

You might want to use while True to create the infinite loop, so your code would be like this:

while True:
 champ = input("Guess a champion: ")
 champ = str(champ)
 found_champ = False
 for i in listC:
 if champ == i:
 found_champ = True
 if found_champ:
 print("Correct")
 else:
 print("Incorrect")