Python runs a if-case that it should not!

Question

I have this code:

def random_answerlist(self):
    self.li = []
    self.winning_button = random.randint(0, 3)
    i = 0
    while i < 20 and len(self.li) is not 4:
        if i == self.winning_button:
            self.li.append(self.flags[self.current_flag][0])
        else:
            new_value = self.random_value()
            if self.flags[new_value][0] not in self.li:
                self.li.append(self.flags[new_value][0])
        i += 1
    return self.li

The only problem with it is that the first if-case may happen several times which should be impossible. I have searched for a good explanation to this and I can't find any.

Oh, I know the code isn't the best. But I'm kind of new to python (just a month or so) and thought this might work, but it didn't!

Do you guys know why? =)

Answer 1

Yes, sorry.

I were out smoking when I realized I were the one failing:

The problem is not the if-case as you guys stated. The problem is that the else case generates randomly from the same list as the first if-case does. And then the same value is getting into the list sometimes as the one in the first if-case.

You couldn't solve it since I didn't post the whole code.

Well thanks anyway :)

Answer 2

One glaring problem is the usage of is not for a value comparision against len(self.li). The tests is not and != are not the same. is tests for identity (are these references to the same object?), != tests for equality (do these objects have the same value?).

Change your while to:

while i < 20 and len(self.li) != 4:

Does that address the issue?