Finding if a reversed string has a match in a list of strings

Question

I am learning Python, one month in and I am struggling with the following problem:

An ice cream shop has a list of flavors:

FLAVORS = [ "Banana", "Chocolate", "Lemon", "Pistachio", "Raspberry", "Strawberry", "Vanilla", ]

They want to build a list of all the alternatives of a 2 balls flavoured ice creams. The flavours cannot be repeated: ie. Chocolate Banana cannot be listed as Banana Chocolate is already in the list. I have to print the list.

Here's my code:

result = []
sub_result = ""

for ice in FLAVORS:
       for other_ice in FLAVORS:
            
            if ice == other_ice:
                continue
                
            sub_result = ice + ", " + other_ice

            if reversed(sub_result) in result:
                continue
        
            result.append(sub_result)
        
print ('\n'.join([item for item in result ])) '''

I cannot get the script to bypass the reversed iteration of the favours.

Answer 1

First of all, reversed reverses an iterable. It returns an iterator, not a string! And you don't want to reverse the string, because that would give you things like 'nomeL ,etalocohC' .

Secondly, make use of the fact that you already know which items you already have in the reverse order!

FLAVORS = [ "Banana", "Chocolate", "Lemon", "Pistachio", "Raspberry", "Strawberry", "Vanilla"]

result = []

for i, ice in enumerate(FLAVORS):
       for other_ice in FLAVORS[i + 1:]:
            result.append(f'{first_flavor} {second_flavor}')
        
print('\n'.join(result))

Answer 2

Using sub_result = ice + ", " + other_ice makes sub_result a string. For example, for Banana and Chocolate , you get 'Banana, Chocolate' . You need ('Banana', 'Chocolate') .

You need to use a tuple or list instead:

sub_result = tuple(reversed((ice, other_ice)))

Notice the cast to tuple - This is because reversed returns an object, not the reverse of the input. The object has to interpreted as the required type.