So I’m trying to make a list of numbers that are multiples of 3, this is my code:
multiples_of_3 = []
for value in range(3, 31):
number = value % 3 == 0
multiples_of_3.append(number)
print(multiples_of_3)
But it transforms the results into booleans, which throws me a list with false and trues instead of numbers, what I’m doing wrong? I know comprehension lists exist and that this could be done more efficiently but well, I’m trying to learn and writing it as a comprehension list doesn’t make it easier.
Your problem is this statement:
number = value % 3 == 0It gets evaluated in this order:
number = (value % 3 == 0)So, first
value % 3 == 0gets evaluated to True or False, and then that gets assigned to the variablenumber.If you only want to append numbers that are multiples of 3, you would need an if-statement, like this:
multiples_of_3 = [] for value in range(3, 31): if value % 3 == 0: multiples_of_3.append(value) print(multiples_of_3)I thought of using an if, but I’m reading a book called “Python Crash Course” and he hasn’t gone over if statements yet, so I thought there has to be a way to express it only using for statements. I have some more knowledge than what was already presented to me in the book from college, but I’m trying to follow the book’s reasoning so far.
In that case, I think you have to use a different approach, and rather than iterate over all the numbers and filter out the ones that aren’t multiples of 3, you can iterate over the multiples of 3 and append every number you iterate over to the array. (Which is what snek_boi’s answer suggests.)
Code for a possible solution, I'm hiding it behind a spoiler because I assume you want to try yourself
multiples_of_3 = [] for value in range(3,31,3): multiples_of_3.append(value) print(multiples_of_3)
The range function has a “step” parameter. You can use it. That way you go from 3 to 31 stepping 3 by 3.
You are appending the result of the comparison value % 3 == 0 to the list multiples_of_3, which will always be either True or False. Instead, you should be appending value to the list if it is a multiple of 3. You can do this by changing the line multiples_of_3.append(number) to multiples_of_3.append(value) if the if statement number = value % 3 == 0 is true.
To add, OP could just use range(3,31,3) which increments by 3. Which reduces the loop enough that it becomes clear something like list comprehension would, yes, be easier.
Edit: Didn’t realize this was 6 months old haha
You’re assigning value % 3 == 0 to number, which evaluates to a boolean instead of a number. Instead of adding the result of that boolean expression, I’d use that boolean expression as a condition for an if and, if true, append value.
I thought of using an if, but I’m reading a book called “Python Crash Course” and he hasn’t gone over if statements yet, so I thought there has to be a way to express it only using for statements. I have some more knowledge than what was already presented to me in the book from college, but I’m trying to follow the book’s reasoning so far.
It’s because the
numbervariable is a boolean, equal to “is value % 3 zero?”. You’re appending that result to the list for every number.What you want is:
multiples_of_3 = [] for value in range(3, 31): if value % 3 == 0: multiples_of_3.append(value) print(multiples_of_3)The if statement means that you only append to the list if it’s a multiple.
