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I do not understand why this function reverses the string

This function requests a string input and reverses it. For some reason, I just cannot wrap my head around the logic behind it.
def reverse(s):
new = ""
for i in s:
print(new)
new = i + new
return new
oldStr = input("String?")
newStr = reverse(oldStr)
print(newStr)
print(reverse("good bye"))
A friend suggested I print the variable new in the string which I added and it helped a little, but I just don't understand it.

It looks to me as if you are in a stage where you want to learn how to debug small programs.
For questions on StackOverflow, you want to provide a minimal reproducible example. What does that mean in your case?
"repoducible" means that you should not depend on user input. Replace user input by hardcoded values.
"minimal" means that you don't call the function twice. Once is enough.
For that reason, I'll not walk you through your original program, but through this one instead:
def reverse(s):
new = ""
for i in s:
print(new)
new = i + new
return new
print(reverse("abcdef"))
I'll use a free program called PyCharm Community Edition. You set a breakpoint where you want to understand how things work. Since you don't understand the reverse() method, put it right at the beginning of that method. You do that by clicking between the line number and the text:
Even if your code has no bug, go to the Run/Debug menu:
Execution will stop at the breakpoint and you'll now be able to see all the variables and step through your code line by line.
Look at all the variables after each single line. Compare the values to what you think the values should be. If there is a mismatch, it's likely a misunderstanding on your side, not by Python. Do that a few times and it'll be obvious why and how the string is reversed.

Let analysis it:
Iteration 1:
new = 'A', i = g
Perform new = i + new : new = gA
Iteration 2:
new = gA, i = o
Perform new = i + new: new = ogA
.
.
.
This happens because we add new i before we add the existing string from previous iteration.

the key is in "new = i + new" note that new is the previous iteration character and is in the right side of the current character, this cause the string to reverse

creating multiple iteration of the same code

beginer question:
I often have to repeat the same line of code 10 times for 10 different variables (i read you can't or should not create variable dynamically)
I thought to help me once i written it once I could iterate with a find replace (I am currently doing it in word)
I wrote this but get tons of error when i input code like if console trying to execute the code. what am i missing? is it because i paste it i the console does it need to be imported from a ext file ?
LineOfCode = input("Enter the code you want to iterate the iteration variable need be 8")
for i in range(10):
LineOfCode.replace("8",str(i))
print(LineOfCode)

Your code is almost correct:
String.replace() returns a new string with the changes, doesn't change the existing string. So the code should be like:
LineOfCode = input("Enter the code you want to iterate the iteration variable need be 8")
for i in range(10):
var = LineOfCode.replace("8", str(i))
print(var)
The question isn't clear enough, so if this isn't what you wanted, edit the question.
Besides this, you can use Visual Code as an IDE, it'll make things much, much easier than Word.
About the errors, I think you might be trying to run the code directly in console. Instead of typing only the file name, type python file.py, assuming the file name is file. The file must be a python file (ending with .py), also it shouldn't be saved as a word file. It must be plain text.

If you want to run the same code on multiple variables, you can create the code as a string, and then use the builtin exec to execute it. Example:
a = 1
b = 2
c = 3
variables = ["a", "b", "c"]
for var in variables:
exec("print(" + var + ")") # print the variable before modifying
exec(var + " *= 2") # multiply the current variable by 2
exec("print(" + var + ")") # print the variable after modifying
If this is not what you need, your question was not clear enough and i misunderstood it, you just have to provide more information on what excatly you need by adding a comment under your question, in which you first type #Programmer and then your text.

Python function not working with seemingly correct string path

I have the following code (it changes the string/filepath, replacing the numbers at the end of the filename + the file extension, and replaces that with "#.exr")
I was doing it this way because the name can be typed in all kinds of ways, for example:
r_frame.003.exr (but also)
r_12_frame.03.exr
etc.
import pyseq
import re
#create render sequence list
selected_file = 'H:/test/r_frame1.exr'
without_extention = selected_file.replace(".exr", "")
my_regex_pattern = r"\d+\b"
sequence_name_with_replaced_number = re.sub(my_regex_pattern, "#.exr" ,without_extention)
mijn_sequences = fileseq.findSequencesOnDisk(sequence_name_with_replaced_number)
If I print the "sequence_name_with_replaced_number" value, this results in the console in:
'H:/test/r_frame#.exr'
When I use that variable inside that function like this:
mijn_sequences = fileseq.findSequencesOnDisk(sequence_name_with_replaced_number)
Then it does not work.
But when I manually replace that last line into:
mijn_sequences = fileseq.findSequencesOnDisk('H:/test/r_frame#.exr')
Then it works fine. (it's the seems like same value/string)
But this is not an viable option, the whole point of the code if to have the computer do this for thousands of frames.
Anybody any idea what might be the cause of this?
After this I will do simple for loop going trough al the files in that sequence. The reason I'm doing this workflow is to delete the numbers before the .exr file extensions and replace them with # signs. (but ognoring all the bumbers that are not at the end of the filename, hence that regex above. Again, the "sequence_name_with_replaced_number" variable seems ok in the console. It spits out: 'H:/test/r_frame#.exr' (that's what I need it to be)

I fixed it. the problem as stated was correct, every time I did a cut and past from the variable value in the console and treated it as manual input it worked.
Then I did a len() of both values, and there was a difference by 2! What happend? The console added the ''
But in the generated variable it had those baked in as extra letters. i fixed it by adding cleaned_sequence = sequence_name_with_replaced_number[1:-1] so 'H:/test/r_frame1.exr' (as the console showed me) was not the same as 'H:/test/r_frame1.exr' (what I inserted manually, because I added these marks, in the console there are showed automatically)

How to save a changed item to an external file? (Python 3)

I'm fairly new to python, but I'm making a script and I want one of the functions to update a variable from another file. It works, but when I exit the script and reload it, the changes aren't there anymore. For example (this isn't my script):
#File: changeFile.txt
number = 0
#File: changerFile.py
def changeNumber():
number += 1
If I retrieve number during that session, it will return 1, but if I exit out and go back in again and retrieve number without calling changeNumber, it returns 0.
How can I get the script to actually save the number edited in changeNumber to changeFile.txt? As I said, I'm fairly new to python, but I've looked just about everywhere on the Internet and couldn't really find an answer that worked.
EDIT: Sorry, I forgot to include that in the actual script, there are other values.
So I want to change number and have it save without deleting the other 10 values stored in that file.

Assuming, as you show, that changeFile.txt has no other content whatever, then just change the function to:
def changeNumber():
global number # will not possibly work w/o this, the way you posted!
number += 1
with open('changeFile.txt', 'w') as f:
f.write('number = {}\n'.format(number))
ADDED: the OP edited the Q to mention (originally omitted!-) the crucial fact that changefile.txt has other lines that need to be preserved as well as the one that needs to be changed.
That, of course, changes everything -- but, Python can cope!-)
Just add import fileinput at the start of this module, and change the last two lines of the above snippet (starting with with) to:
for line in fileinput.input(['changefile.txt'], inplace=True):
if line.startswith('number ');
line = 'number = {}\n'.format(number)'
print line,
This is the Python 2 solution (the OP didn't bother to tell us if using Py2 or Py3, a crucial bit of info -- hey, who cares about making it easy rather than very hard for willing volunteers to help you, right?!-). If Python 3, change the last statement from print line, to
print(line, end='')
to get exactly the same desired effect.

Using Strings to Name Hash Keys?

I'm working through a book called "Head First Programming," and there's a particular part where I'm confused as to why they're doing this.
There doesn't appear to be any reasoning for it, nor any explanation anywhere in the text.
The issue in question is in using multiple-assignment to assign split data from a string into a hash (which doesn't make sense as to why they're using a hash, if you ask me, but that's a separate issue). Here's the example code:
line = "101;Johnny 'wave-boy' Jones;USA;8.32;Fish;21"
s = {}
(s['id'], s['name'], s['country'], s['average'], s['board'], s['age']) = line.split(";")
I understand that this will take the string line and split it up into each named part, but I don't understand why what I think are keys are being named by using a string, when just a few pages prior, they were named like any other variable, without single quotes.
The purpose of the individual parts is to be searched based on an individual element and then printed on screen. For example, being able to search by ID number and then return the entire thing.
The language in question is Python, if that makes any difference. This is rather confusing for me, since I'm trying to learn this stuff on my own.
My personal best guess is that it doesn't make any difference and that it was personal preference on part of the authors, but it bewilders me that they would suddenly change form like that without it having any meaning, and further bothers me that they don't explain it.
EDIT: So I tried printing the id key both with and without single quotes around the name, and it worked perfectly fine, either way. Therefore, I'd have to assume it's a matter of personal preference, but I still would like some info from someone who actually knows what they're doing as to whether it actually makes a difference, in the long run.
EDIT 2: Apparently, it doesn't make any sense as to how my Python interpreter is actually working with what I've given it, so I made a screen capture of it working https://www.youtube.com/watch?v=52GQJEeSwUA

I don't understand why what I think are keys are being named by using a string, when just a few pages prior, they were named like any other variable, without single quotes
The answer is right there. If there's no quote, mydict[s], then s is a variable, and you look up the key in the dict based on what the value of s is.
If it's a string, then you look up literally that key.
So, in your example s[name] won't work as that would try to access the variable name, which is probably not set.
EDIT: So I tried printing the id key both with and without single
quotes around the name, and it worked perfectly fine, either way.
That's just pure luck... There's a built-in function called id:
>>> id
<built-in function id>
Try another name, and you'll see that it won't work.

Actually, as it turns out, for dictionaries (Python's term for hashes) there is a semantic difference between having the quotes there and not.
For example:
s = {}
s['test'] = 1
s['othertest'] = 2
defines a dictionary called s with two keys, 'test' and 'othertest.' However, if I tried to do this instead:
s = {}
s[test] = 1
I'd get a NameError exception, because this would be looking for an undefined variable called test whose value would be used as the key.
If, then, I were to type this into the Python interpreter:
>>> s = {}
>>> s['test'] = 1
>>> s['othertest'] = 2
>>> test = 'othertest'
>>> print s[test]
2
>>> print s['test']
1
you'll see that using test as a key with no quotes uses the value of that variable to look up the associated entry in the dictionary s.
Edit: Now, the REALLY interesting question is why using s[id] gave you what you expected. The keyword "id" is actually a built-in function in Python that gives you a unique id for an object passed as its argument. What in the world the Python interpreter is doing with the expression s[id] is a total mystery to me.
Edit 2: Watching the OP's Youtube video, it's clear that he's staying consistent when assigning and reading the hash about using id or 'id', so there's no issue with the function id as a hash key somehow magically lining up with 'id' as a hash key. That had me kind of worried for a while.