How to compare a string with a list in python

Question

I would like to compare a string with a list, but my code isn't working

def compare(typeOfColors):
   introduceC = input("Introduce a color")
   while(introduceC.lower() != typeOfColors)
       print("Error")
colors = ["white", "black"] 
compare(colors)

Are you aware of the for statement? docs.python.org/3/tutorial/controlflow.html#for-statements — Random Davis
– Random Davis, Commented Dec 2, 2020 at 18:23
introduceC.lower() in typeOfColors is enough to know if the lower version of the input string is present in the list — bruno
– bruno, Commented Dec 2, 2020 at 18:24

bruno · Accepted Answer · 2020-12-02 18:39:38Z

1

To know if a string is in typeOfColors just use in

Note introduceC is unchanged in your loop, so if introduceC.lower() != typeOfColorsis false you loop without ending

To loop until the input is part of the list you can just do

def compare(typeOfColors):
   while (not input("Introduce a color: ").lower() in typeOfColors):
       print("Error")

compare(["white", "black"])

Example

Python 3.7.3 (default, Jul 25 2020, 13:03:44) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def compare(typeOfColors):
...    while (not input("Introduce a color: ").lower() in typeOfColors):
...        print("Error")
... 
>>> compare(["white", "black"])
Introduce a color: blue
Error
Introduce a color: red
Error
Introduce a color: bLack
>>>

answered Dec 2, 2020 at 18:39

bruno

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Comments

Martin Kleiven · Accepted Answer · 2020-12-02 18:48:31Z

1

Use the in keyword to test if an array contains a value.

def compare(typeOfColors):
   introduceC = input("Introduce a color")
   while introduceC.lower() not in typeOfColors:
       print("Error")
colors = ["white", "black"] 
compare(colors)

But that introduces a new error, infinite looping, which you could solve like this:

def compare(typeOfColors):
    introduceC = input("Introduce a color: ")
    if introduceC.lower() not in typeOfColors:
       print("Error")
       return compare(typeOfColors)

    print('Exists!')
    return introduceC

colors = ["white", "black"] 
compare(colors)

Giving:

Introduce a color: red
Error
Introduce a color: blue
Error
Introduce a color: whitE   
Exists!

If the user inputs something that is not in the accepted values, the function calls itself, effectively restarting. That is recursion.

edited Dec 2, 2020 at 18:48

answered Dec 2, 2020 at 18:25

Martin Kleiven

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4 Comments

bruno Over a year ago

introduceC never change => you loop without ending if the test is false

Martin Kleiven Over a year ago

@bruno, I did mention as much, in any case I gave a more complete solution now.

BRT 88 Over a year ago

Thanks, but i want the program to ask again for a color if its not in the list

Martin Kleiven Over a year ago

@BRT88 It does ask again, try it!

Danyman · Accepted Answer · 2020-12-02 18:22:55Z

0

Try looping through each element of the list. Then for each element comparing that with the color.

I'll try to help you if you need more than that.

answered Dec 2, 2020 at 18:22

Danyman

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3 Comments

bruno Over a year ago

there is no need top loop on the list, in will do that for you

BRT 88 Over a year ago

But if i do a for loop, maybe the correct color is the last one, but i will have previous "Error" messages from the others

Danyman Over a year ago

I don't really understand what you want then.

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