Need help with this beginner's code for Python.

[LebowskiBuschemi]

So I recently got into Python and I'm learning about Boolean logic. I was doing this exercise and I came upon this question that involved a customer getting one of three toppings. What's confusing me is how it's equal to 1 in Boolean logic if the customer's gotten only one topping. Is the 1 implying that since 0+0+1 is equal to 1, only one topping was put?

 

 

[BobVonBob]

You've got it right, the == there is integer equality. It's converting the boolean variables to integers, specifically 0 for false and 1 for true, and adding those together. The sum (ketchup + mustard + onion) is equal to the total number of those variables that are true, so if the final value is one then only one variable is true, which is what that function is looking for.

[Kilrah]

Yes. A boolean converted to int is 1 if true and 0 if false, so if you're comparing the sum with 1 that will only be true if there's one and only one that's true.

[noitcelfeR]

On 12/3/2021 at 9:37 AM, LebowskiBuschemi said:

So I recently got into Python and I'm learning about Boolean logic. I was doing this exercise and I came upon this question that involved a customer getting one of three toppings. What's confusing me is how it's equal to 1 in Boolean logic if the customer's gotten only one topping. Is the 1 implying that since 0+0+1 is equal to 1, only one topping was put?

 

 

This is a confusing problem. I've never seen anyone implicitly cast a boolean to an int to make the function shorter. Doing

exactly_one_topping(ketchup, mustard, onion)

, the arguments are positional. This is not very Pythonic. What if you wanted to add lettuce or cheese? You can see how the arguments can add up pretty quickly! Also, it could get difficult to maintain. 

 

The more pythonic way to do this would probably be 

def exactly_one_topping(**toppings):
  """Returns true if there is exactly one topping. 
  """
  has_topping = False  # No toppings
  for _, val in toppings:  # _ is the standard convention for skipping a value in a tuple
    if val: 
      if has_topping:
        return False  # Too many toppings
      has_topping = True  # One topping
  
  return has_topping

I'm not sure where these examples are coming from. Where are they?

[Kilrah]

9 hours ago, noitcelfeR said:

the arguments are positional. This is not very Pythonic. What if you wanted to add lettuce or cheese? You can see how the arguments can add up pretty quickly! Also, it could get difficult to maintain. 

 

I'm not sure where these examples are coming from. Where are they?

The OP mentioned that the point was to show how booleans and their conversions worked, not to make "clean" code...

[tikker]

13 hours ago, noitcelfeR said:

I've never seen anyone implicitly cast a boolean to an int to make the function shorter.

I use it all the time. Not specifically to make the function shorter by those precious 3 characters, but it's just nice and convenient that 0, empty lists, tuples and dictionaries, etc. all evaluate to False or 0. Makes for easy "if not X: <bla>" checks and some easy counting.