How to check if a string is inside a string set?

Question

In the code below I have the set of strings ('M', 'F') and soon after I ask the user to enter their gender so that the value is recorded.

valores = ('M','F')
print(valores)

sexo = str(input('Digite o seu sexo [M/F]: ')).upper()[0].strip()
print(sexo)

if sexo == valores:
    print('Valor registrado com sucesso.')
else:
    print('Dados incorretos. Digite novamente.')

I want to check if the user’s answer is within the values I set, but I can’t do it because even if I type the correct value, it says it’s wrong. See below:

('M','F')
Digite o seu sexo [M/F]: m
M
Dados incorretos. Digite novamente.

Why is this happening? How can I check whether the value is valid or not ?

Answer 1

I didn’t quite understand the "use string as value" part, but rather it is possible to check whether a string is inside a list, tuple and other iterable.

In your example code, the comparison returned False because a string is different of a tuple containing strings, as well as "1" is different from 1. To check if a string is inside an iterable (in your case a string tuple), you must replace the operator == for in. See how it would look:

valores = ('M', 'F')
print(valores)

sexo = input('Digite o seu sexo [M/F]: ').upper()[0].strip()
print(sexo)

if sexo in valores:
    print('Valor registado com sucesso.')
else:
    print('Dados incorretos. Digite novamente.')

The operator in unlike ==, checks whether an object (can be an object of any type) is inside an eternal, or rather, it checks whether the target object contains the object you are specifying.

You can do this check not only with strings, but also with objects of other types. See the examples below:

"Masculino"  in  ["Masculino", "Feminino"]          # True
17           in  [19, 23, 3, 1023, 17, 65]          # True
3            in  ["3", 2, True, "bola"]             # False ("3" é diferente de 3)
True         in  [False, True, False, False]        # True

Remember I told you in checks if an object contains an element ? Then... this verification occurs through the method __contains__ that takes a value and checks whether or not the object is passed. Example:

class MinhaClasse():
    def __contains__(self, value):

        if value == 7:
            return True
        else:
            return False

objeto = MinhaClasse()

3 in objeto  # False
7 in objeto  # True

Note that the object to be checked is always before the operator. So if I reversed the code to objeto in 7, I’d be checking if the object is in the number 7 and besides not working, would still generate an error, because int does not have the method __contains__.