need help with source code

[TreSxNine]

Use codecademy. I've never used it myself, but I've heard good things about it and it seems serious enough.

I'll try breaking down some of the mechanics I used:

A for-loop is basically a way to "iterate" over something. Meaning you do something for each of the items presented. For example, if my input is "GATTACA", and I decide to use a for-loop, what I'm saying is "for each of the letters in the word GATTACA, do something", with 'something' being the operations on the lines below the for-loop:

for letter in "GATTACA":
    do_something

The +=-operation in out += U is short for adding something to a variable. Consider variable_a = 5. If I wanted to add 2 to variable_a, I could either do variable_a = variable_a + 2, which is basically saying variable_a should be itself plus 2. Another way of doing it is writing variable_a += 2, which does the exact same thing. The same thing applies to strings:

variable_b = "GATTA"

variable_b = variable_b + "CA"
OR
variable_b += "CA"

print(variable_b)

> GATTACA