Python sum of elements

Can some one explain me this code? I can't understand why sumOfLetter for i in inputText for sumOfLetter. What does second "for" do?

sum([sumOfLetter for i in inputText for sumOfLetter, weigthOfCh in pointsInRu.items() if i in weigthOfCh])

I find this code for my solution, changed variable names and it's work correct, but don't understand how it works.

This notation is shorthand for the code below. The square brackets show there's a list being created and directly used for the sum() function. Since the list is created and directly used, there's no variable and also no append() (this is done implicitely).

new_list = []
for i in inputText:
  for sumOfLetter, weigthOfCh in pointsInRu.items():
    if i in weigthOfCh:
      new_list.append(sumOfLetter)

sum(new_list)

Not a python expert, but i think this is what is going on:

pointsInRu is a key-value pair (dictionary might be what it is called) that contains letters as keys.

inputText self explanatory.

[sumOfLetter for i in inputText for sumOfLetter, weigthOfCh in pointsInRu.items() if i in weigthOfCh] is where things get sketchy, its a list comprehension that iterates over each character i in inputText, and for each character, it checks if it exists in the keys of pointsInRu. If it does, then it extracts the corresponding value weigthOfCh and appends it to a list called sumOfLetter.

Then the sum() function is used to sum up all the values in the sumOfLetter list and return the total value.

To be fair, this is pretty nasty code, let's give it a go:

1. The original code:

sum([sumOfLetter for i in inputText for sumOfLetter, weigthOfCh in pointsInRu.items() if i in weigthOfCh])

2. The above is equivalent to this:

my_values = [sumOfLetter for i in inputText 
            for sumOfLetter, weigthOfCh in pointsInRu.items() 
            if i in weigthOfCh]

sum(my_values)

To go further I'll make some assumptions,

inputText is some fixed string
pointsInRu is a dictionary mapping a number to a string (?)

Then:

my_values = [sumOfLetter for i in inputText 
            for sumOfLetter, weigthOfCh in pointsInRu.items() 
            if i in weigthOfCh]

is equivalent to:

my_values  = []

for i in inputText:
   for sumOfLetter, weigthOfCh in pointsInRu.items():
      if i in weigthOfCh:
          my_values.append(sumOfLetter)

This code illustrates the syntax that is being used:

[f'{i=}{j=}' for i in [1,2,3] for j in [5,6,7]]

>>> [
 'i=1j=5',
 'i=1j=6',
 'i=1j=7',
 'i=2j=5',
 'i=2j=6',
 'i=2j=7',
 'i=3j=5',
 'i=3j=6',
 'i=3j=7']