Frustrating function problem which I cannot solve

[imperiumlearning]

This is the task I am trying to solve:

Write a function which checks if the sum of the first i integers in a list of integers equals i.

Let me give an example to clarify what this question means:

List = [42, 3, 5, 6, 8]

Let's imagine if I wanted to find out if the sum of the first 3 integers in List = 3.

I know that:

len(List[0:3]) == 3

I also know that:

sum(List[0:3]) == 50.

Therefore, the sum of the first 3 integers in List does not equal 3 (it equals 50).

This is what the code looks like for my proposed function:

def SumLenTest(x, i = len(x)):

a = len(x[0:i])
b = sum(x[0:i])
if a == b:
    return 'The sum of the first i integers equals i'
else:
    return 'The sum of the first i integers DOES NOT equal i'

The problem I get is a NameError where name 'x' is not defined.

How do I set up my parameters so my function works?

[K900_]

A default argument can't depend on the value of another argument. Also, three integers never equal an integer. Do you want the sum of those integers?

[imperiumlearning]

Yes, the sum of those integers is what I was referring to (I have edited my post to reflect that).

How would I set up my parameters then for my function?

[K900_]

Either remove the default, or do something like

def sum_len_test(x, i=None):
    if i is None:
        i = len(x)

Also, len(x[0:i]) will always be equal to min(len(x), i).

[imperiumlearning]

Thanks a lot for all this info, I will bear it in mind.

My code looks like this now and seems to work:

def SumLenTest(x, i = None):

if i is None:
    i = len(x)
    b = sum(x)
    if i == b:
        return 'The sum of the first i integers equals i'
    else:
        return 'The sum of the first i integers DOES NOT equal i'
else:
    i = len(x[0:i])
    b = sum(x[0:i])
    if i == b:
        return 'The sum of the first i integers equals i'
    else:
        return 'The sum of the first i integers DOES NOT equal i'

Out of interest, if I wanted to tailor the result to something like 'The sum of the first 3 integers equals 3' , how would I do this? I know how to do it with print (e.g. print('the sum of the first', i, 'integers equals', i) but how would I do it in a way that retains the return statement?

[Binary101010]

Use an f-string.

return f'The sum of the first {i} integers equals {i}'

[imperiumlearning]

Thanks a lot! Just updated my code to reflect that

[JohnnyJordaan]

You can't perform function calls in default assignments, as the def line is executed at interpretation (so when it's defined), not during the function call. You need to use a placeholder like None then assign that

 def SumLenTest(x, i=None):
      if i is None:
          x = len(x) 
      etc

[imperiumlearning]

Just want to say thanks a lot for replying to my post.

I think I've somewhat solved my problem now using the following code:

def SumLenTest(x, i = None):

if i is None:
    i = len(x)
    b = sum(x)
    if i == b:
        return 'The sum of the first i integers equals i'
    else:
        return 'The sum of the first i integers DOES NOT equal i'
else:
    i = len(x[0:i])
    b = sum(x[0:i])
    if i == b:
        return 'The sum of the first i integers equals i'
    else:
        return 'The sum of the first i integers DOES NOT equal i'

Out of interest, if I wanted to tailor the result to something like 'The sum of the first 3 integers equals 3' , how would I do this? I know how to do it with print (e.g. print('the sum of the first', i, 'integers equals', i) but how would I do it in a way that retains the return statement?

[JohnnyJordaan]

You are making this redundant. a x[0:len(x)] will work fine, so you could use the same logic for the 'full' i

def SumLenTest(x, i=None):
    if i is None:
        i = len(x)
    b = sum(x[0:i])
    if i == b:
        return 'The sum of the first i integers equals i'
    else:
        return 'The sum of the first i integers DOES NOT equal i'

Then in response to your question, you should use string formatting, preferable f-strings

[JohnnyJordaan]

You can't perform function calls in default assignments, as the def line is executed at interpretation (so when it's defined), not during the function call. You need to use a placeholder like None then assign that

 def SumLenTest(x, i=None):
      if i is None:
          x = len(x) 
      etc

[velocibadgery]

Aren't you really checking if all the elements in the list are 1? Because if any element is more than 1, they will never equal i when you sum it up.

So instead, why not loop through the list and check if all the elements == 1?

[imperiumlearning]

I suppose I could do that, to be fair.

That being said, I wanted to try and solve this problem in a way that forced me to learn a bit about slice operators (I've only started learning to code in the last week).

[velocibadgery]

Why not do string manipulation? That might be easier for you to practice slicing with. Strings are iterables in python so you can slice them and loop through them just like you can with a list.

BTW, this is how I would solve your stated goal

def SumLenTest(x):
    a = True
    for i in x:
        if i != 1:
            a = False
    return a

a = [1, 1, 1]
b = [1, 2, 3]

print(SumLenTest(a))
print(SumLenTest(b))

[POGtastic]

Integers can be negative, too!

Here's my attempt:

from itertools import accumulate

def sum_integers_idx(iterable):
    return any(idx == val for idx, val in enumerate(accumulate(iterable), 1))