how to get the output of input list, as a list using a formula

Question

i need to print a solution list for the input list using the below formula, this is the code:

sub=[1,2,3,4,5,6,7]
a=[]



for i in sub:
     def res(i):(sub/12)*100 #this is the formula
     a.append(res(i))
print(a)

formula:

(sub/12)*100

i am getting this error:

Traceback (most recent call last):
  File "c:\Users\suh\Desktop\se proj 2\backend.py", line 62, in <module>
    a.append(res(i))
  File "c:\Users\suh\Desktop\se proj 2\backend.py", line 61, in res
    def res(i):(sub/12)*100
TypeError: unsupported operand type(s) for /: 'list' and 'int'

score 2 · Accepted Answer · 2022-02-05T20:43:58.673

There are several things going on here:

First of all, don't define a function inside of a loop. You want to define the function that implements the logic of the formula separately and call it from within the loop. You also need to use return in the function in order to send the calculated value back to whoever called the formula function.

Secondly, you want to go over each element in the sub list, apply the formula on it and then append the result to a list.

In addition, it is a good idea to provide meaningful variable names (a and res are not meaningful).

Applying the above, you get this:

def formula(num):
    return (num / 12) * 100  # this is the formula


sub = [1,2,3,4,5,6,7]
sub_after_formula = []
for num in sub:
     sub_after_formula.append(formula(num))
print(sub_after_formula)

Output:

[8.333333333333332, 16.666666666666664, 25.0, 33.33333333333333, 41.66666666666667, 50.0, 58.333333333333336]

As @JonSG mentioned, it is recommended to use the list comprehension instead of the for loop in cases like this:

sub_after_formula = [formula(x) for x in sub]

For good measure you might add in a note about using `map()` or a comprehension. `sub_after_formula = list(map(formula, sub))` or `sub_after_formula = [formula(x) for x in sub]` as alternate strategies. — JonSG, Feb 05 '22 at 20:37
@JonSG You're right - list comprehension is the way to go here, I'll update my answer accordingly. I believe using `map` here is not a good idea as it is recommended to use list comprehension in cases like this (https://stackoverflow.com/questions/1247486/list-comprehension-vs-map). Thanks — , Feb 05 '22 at 20:42

score 1 · Answer 2 · edited Feb 05 '22 at 21:58

1

sub=[1,2,3,4,5,6,7]    
a=[]    

for i in sub:    
     res = (i/12)*100 #this is the formula    
     a.append(res)    
print(a)

You shouldn't make a function in a for loop. In this example as per me no function is needed. You are getting the error actually because your formula is (sub/12)*100 while sub is a list. i is the item there not sub your formula should be (i/12)*100 You can't divide a list with 12., but an integer which is i here

edited Feb 05 '22 at 21:58

answered Feb 05 '22 at 21:00

ROOP AMBER

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Sorry, I was on the phone so couldn't arrange the code – ROOP AMBER Feb 05 '22 at 21:01
Well, upvote me please – ROOP AMBER Feb 07 '22 at 02:53
1

@ROOPAMBER No worries, happy to help – Feb 07 '22 at 12:27

score 1 · Answer 3 · answered Feb 05 '22 at 21:19

For this small list, the list comprehension / map approach is great.

For a larger list, or if you plan to do more mathematical operations on the list, it might be worth looking into the numpy library. This often results in a significant speed increase, and can simplify the code.

Once you convert the list to a numpy array, you can perform vectorised operations:

sub = [1,2,3,4,5,6,7]
sub_array = np.array(sub)
result = (sub_array/12) * 100
print(result)

Or we can use a function and pass the array directly:

def formula(num):
    return (num / 12) * 100

sub_array = np.array(sub)
result = formula(sub_array)
print(result)

For a slight speed increase, you can use formula(np.fromiter(sub,dtype=np.int32)) from https://stackoverflow.com/a/59509701/9555388

thank you this one works as well – Suhas S Feb 06 '22 at 15:59 — Suhas S, Feb 06 '22 at 15:59

how to get the output of input list, as a list using a formula

3 Answers3