adds rot13
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@ -1220,24 +1220,259 @@ Think of some ways to improve on it.
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Can you limit the number of tries?
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Can you add a feature to let the user play a *second* game after he/she wins or loses?
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Coming up with challenges is on of the most *challenging* aspect op learning how to program.
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Your thought process will send you of into unknown territory and will force you to expand you knowledge!
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Your thought process will send you of into unknown territory and will force you to expand you knowledge.
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We'll get back to this thought process later, but if you feel like an extra challenge go for it!
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# Lists
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The different built-in objects we've seen until now, such as `str` and `int` are simple [text](https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str) and [numeric](https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex) types.
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There are other classes of objects that server different purposes.
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One of these *groups* is called [sequence types](https://docs.python.org/3/library/stdtypes.html#sequence-types-list-tuple-range).
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A list in python is pretty much exactly what you think it is.
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It is an *object* that groups together *other* objects.
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Sounds complicated?
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Have a look at the following.
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```python3
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my_numbers = [1, 2, 44, 60, 70]
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print(my_numbers)
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```
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Easy right?
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Compared to [other languages](https://www.cplusplus.com/reference/list/list/) lists in python are *very* flexible.
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They can contain objects of different types, and their length can be changed at any time.
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Programmers coming from other languages often find this flexibility of python a bug but you should see it as a feature.
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```python3
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favorite_number = 7
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name = "wouter"
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date = [1986, 10, 7]
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values = [1, date, favorite_number, "hello world", name]
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print(values)
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```
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The code above is just an illustration of the flexibility of lists.
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## Creating lists
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## Picking elements
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Creating lists can be done in two ways, either by using the **square brackets** `[]` or by calling `list`.
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When calling `list` it takes **one argument**, which python will iterate over.
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For example:
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## Slicing lists
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```python3
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>>> first_list = ["hello", "world", "!"]
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>>> first_list
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['hello', 'world', '!']
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>>> second_list = list("hello world !")
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>>> second_list
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['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd', ' ', '!']
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>>>
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```
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## List methods
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As a `list` is a different type of object, it has different methods you can invoke on it.
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When using tab complete in the python shell we get the following.
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```python3
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>>> second_list.
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second_list.append( second_list.count( second_list.insert( second_list.reverse(
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second_list.clear( second_list.extend( second_list.pop( second_list.sort(
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second_list.copy( second_list.index( second_list.remove(
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>>> second_list.
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```
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One of the most used methods is `append`.
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It is used to add an element to the end of the list.
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The second most used method is the `pop` one.
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Read the shell code below and you'll understand immediately what they do.
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```python3
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>>> first_list
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['hello', 'world', '!']
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>>> first_list.append("coucou")
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>>> first_list
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['hello', 'world', '!', 'coucou']
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>>> first_list.pop()
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'coucou'
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>>> first_list
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['hello', 'world', '!']
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>>>
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```
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🏃 Try it
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---
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Look at all the methods you can invoke on a list and try them out.
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Remember to read the documentation!
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## Picking elements and slicing lists
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We can pick elements from the list of slice the list as we please.
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A code block speaks more than words.
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```python3
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>>> long_list
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['I', 'am', 'a', 'very', 'long', 'list', 'of', 'words', 'that', 'make', 'little', 'actual', 'sense']
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>>> long_list[7]
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'words'
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>>> long_list[7:9]
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['words', 'that']
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>>> long_list[7:]
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['words', 'that', 'make', 'little', 'actual', 'sense']
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>>> long_list[:7]
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['I', 'am', 'a', 'very', 'long', 'list', 'of']
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>>> long_list[-1]
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'sense'
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>>> long_list[0]
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'I'
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>>>
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```
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⛑ **In programming we start counting at 0 because 0 and nothing are not the same thing.**
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🏃 Try it
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---
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Slice and dice away!
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A handy method of the `str` class is `split` which will cut up a string into separate elements.
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The result will be a `list` on which you can use `list` methods.
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# For loop
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TODO say hello to my friends exercise
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TODO simple ROT13 cryptography with multiple libs
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I mentioned the for loop, which is a loop in space, when we saw the `while` loop.
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The [keyword](https://docs.python.org/3/reference/compound_stmts.html#the-for-statement) in question is, surprise surprise, `for`!
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I see it as a loop in space because it will run *for each element in a sequence* which in my mind is something of substance.
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Your logical mileage may vary but as long as you understand the following code block we're good.
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```python3
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import time
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friends = ["max", "mike", "alice", "steve", "rosa", "hans"]
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print("The door opens and in walk my {} friends!".format(len(friends)))
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for friend in friends:
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print("Hello {}!".format(friend.capitalize()))
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time.sleep(1)
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print("{} closes the door behind him...".format(friend.capitalize()))
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```
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# Coding challenge - Cheerleader chant
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TODO nested for loop exercise
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Can you make me a program that outputs this type of cheerleader chant?
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You can make it *prettier* by importing your `pretty_print` function, plus you can add some `time.sleep` in it to make it more *musical*.
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```
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Give me an m
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M
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Give me an a
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A
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Give me an x
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X
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Gooooooooo, MAX!
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Give me an m
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M
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Give me an i
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I
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Give me an k
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K
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Give me an e
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E
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Gooooooooo, MIKE!
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Give me an c
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C
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Give me an a
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A
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Give me an m
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M
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Give me an i
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I
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Give me an l
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L
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Give me an l
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L
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Give me an e
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E
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Gooooooooo, CAMILLE!
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```
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<details>
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<summary>Spoiler warning</summary>
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```python3
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friends = ["max", "mike", "camille"]
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for friend in friends:
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for letter in friend:
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print("Give me an {}".format(letter))
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print("{}".format(letter.upper()))
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print("Gooooooooo, {}!".format(friend.upper()))
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```
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</details>
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# Coding challenge - ROT13
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ROT13 is one of the oldest cryptographic cyphers know to mankind.
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It dates back to the Roman empire and is also known as a [Caesar cypher](https://en.wikipedia.org/wiki/Caesar_cipher).
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The algorithm is pretty simple, you just shift a letter 13 places in the alphabet so `a` becomes `n` or `x` becomes `k`.
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Have a look at [this](https://rot13.com/) website to see the cypher in action.
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Now, can you make a program that encrypts a phrase with ROT13?
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Something along these lines:
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```python3
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What's your secret? hello world!
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encoded secret: uryyb jbeyq!
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```
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<details>
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<summary>Spoiler warning</summary>
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```python3
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import string
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def encode_rot(msg, rot=13):
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msg = msg.lower()
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letters = list(string.ascii_lowercase)
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coded_msg = []
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for letter in msg:
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if letter not in letters:
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coded_msg.append(letter)
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else:
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idx = letters.index(letter) + rot
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coded_letter = letters[idx % len(letters)]
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coded_msg.append(coded_letter)
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coded_msg = "".join(coded_msg)
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return coded_msg
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def decode_rot(msg, rot=13):
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pass
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if __name__ == "__main__":
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clear_message = input("What's your secret? ")
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encoded_message = encode_rot(clear_message)
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print("encoded secret: {}".format(encoded_message))
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```
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</details>
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🏃 Try it
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---
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To make things more interesting you can add a decode function.
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Plus you could add a prompt that asks how big the shift should be (ROT13, ROT16, ...).
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# List comprehension
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This is a bit of an advanced topic but I'm putting it here to show you a very unique and powerful feature of python.
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# Handling files
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