Added Python Explanation

Author: hrszpuk

Python/README.md

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+# Caesar Cipher in Python
+In this code challenge we are implementing the famous Caesar cipher used to send messages without a third-party being able to read them. 
+
+## Problem
+Implement a Caesar cipher, both encoding and decoding. The key is an integer from 1 to 25. This cipher rotates the letters of the alphabet (A to Z). The encoding replaces each letter with the 1st to 25th next letter in the alphabet (wrapping Z to A). So key 2 encrypts “HI” to “JK”, but key 20 encrypts “HI” to “BC”.
+
+## Solution
+The caesar cipher is a substitution cipher; a cipher where each letter in the alphabet is replaced with another.
+This makes understanding the cipher quite easy.
+
+### Caesar Cipher Explanation
+We have 26 letters in the alphabet. 
+When we "shift" the letters along the order of the letters change.
+In our cipher, we replace any letters in the previous position with the letters in the shifted position.
+We can use the sentence `THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG` to show this.
+```python
+Alphabet: A B C D E G F H I J K L M N O P Q R S T U V W X Y Z
+Text: THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
+Shift all letters by 1
+New alphabet: Z A B C D E G F H I J K L M N O P Q R S T U V W X Y
+Text: UIF RVJDL CSPXO GPY KVNQT PWFS UIF MBAZ EPH
+```
+Look how unreadable the text has become after simply replacing the letters with the next letter in the alphabet!
+Decoding the encoded text back into plaintext is simple: we apply the cipher in the opposite direction.
+So for example, if we encode "APPLE" to "KZZVO" (shifting 10 places) we can turn "KZZVO" back to "APPLE" by shifting -10 places.
+
+Read more:
+- [Wikipedia page on the Caesar Cipher](https://en.wikipedia.org/wiki/Caesar_cipher)
+- [Online Caesar Cipher converter](https://cryptii.com/pipes/caesar-cipher)
+
+## Python Solution Explained
+
+```python
+# define the data we need: alphabet, text, shift amount.
+alphabet = "abcdefghijklmnopqrstuvwxyz"
+# .lower() is used to convert the text into only lower text as our alphabet only has lowercase letters.
+text = input("Please enter your text: ").lower()
+# make sure to use int() so our shift is a number not a string.
+shift_amount = int(input("Please enter the shift amount: ")) 
+```
+```python
+# This is very similar to the pseudocode example .
+new_text = ""
+for letter in text:
+    if letter in alphabet:
+        # We shift the letter only if it is in the alphabet.
+        index = alphabet.index(letter)
+        index += shift_amount
+        index %= 26
+        new_text += alphabet[index]
+    else:
+        # Just add any numbers/symbols/etc onto the encoded text .
+        new_text += letter
+```
+```
+# Show the difference between the original and encoded text.
+print(f"\"{text}\" has been encoded to \"{new_text}\"")
+```

Python/solution.py

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+
+# define the data we need: alphabet, text, shift amount.
+alphabet = "abcdefghijklmnopqrstuvwxyz"
+# .lower() is used to convert the text into only lower text as our alphabet only has lowercase letters.
+text = input("Please enter your text: ").lower()
+# make sure to use int() so our shift is a number not a string.
+shift_amount = int(input("Please enter the shift amount: "))
+
+# This is very similar to the pseudocode example .
+new_text = ""
+for letter in text:
+    if letter in alphabet:
+        # We shift the letter only if it is in the alphabet.
+        index = alphabet.index(letter)
+        index += shift_amount
+        index %= 26
+        new_text += alphabet[index]
+    else:
+        # Just add any numbers/symbols/etc onto the encoded text .
+        new_text += letter
+
+# Show the difference between the original and encoded text.
+print(f"\"{text}\" has been encoded to \"{new_text}\"")

README.md

@@ -1,4 +1,4 @@
-# CaesarCipher
+# Caesar Cipher
 In this code challenge we are implementing the famous Caesar cipher used to send messages without a third-party being able to read them. 
 
 ![GitHub followers](https://img.shields.io/github/followers/hrszpuk?style=social)
@@ -30,27 +30,66 @@ New alphabet: Z A B C D E G F H I J K L M N O P Q R S T U V W X Y
 Text: UIF RVJDL CSPXO GPY KVNQT PWFS UIF MBAZ EPH
 ```
 Look how unreadable the text has become after simply replacing the letters with the next letter in the alphabet!
+Decoding the encoded text back into plaintext is simple: we apply the cipher in the opposite direction.
+So for example, if we encode "APPLE" to "KZZVO" (shifting 10 places) we can turn "KZZVO" back to "APPLE" by shifting -10 places.
 
 Read more:
 - [Wikipedia page on the Caesar Cipher](https://en.wikipedia.org/wiki/Caesar_cipher)
 - [Online Caesar Cipher converter](https://cryptii.com/pipes/caesar-cipher)
 
 ### Pseudo code solution
+To get started, the code here is written in pseudocode which isn't a programming language, but a language that is simple 
+and easy to read, so anyone can read it and understand the logic behind the code. 
+After understanding the logic implementing your own version of the code in your preferred programming language becomes easier.
 
+First off, we declare a few variables: alphabet, which is a list containing all the letters in the alphabet.
+We also get the text the user wants encoding, and the shift amount which is the amount of letters we will shift each letter.
 ```python
 alphabet = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']
 text = INPUT
 shift_amount = INPUT
 ```
 
+Next it's time to actually encode the text.
+We define `new_text` which will store the encoded text.
+For each letter in text we do the following:
+1. Get the index of that letter in the alphabet (e.g. a is 1, b is 2, c is 3, ...etc)
+2. We add the `shift_amount` to the index (if our letter was "a" so an index of 1 it would now be 1 + `shift_amount`)
+3. Then we use `mod` (short for [modulo](https://www.mathsisfun.com/definitions/modulo-operation.html)) to ensure the `index` is within 26 (which is the range of our alphabet).
+4. And finally, we add the new letter to `new_text` but getting the letter at that index of the alphabet (e.g. alphabet[1] = a)
+
+After we have looped over every letter in the `text` we output `new_text` which is our encoded text.
 ```python
 new_text = EMPTY STRING
-FOR EACH letter IN text:
+FOR EACH letter IN text
     index = INDEX OF letter IN alphabet
-    index = index + SHIFT_AMOUNT
+    index = index + shift_amount
     index = index MOD 26
     new_text = new_text + alphabet[index]
 END
 
 OUTPUT new_text
 ```
+
+It's important to read the problem carefully, in this code challenge we must encode **and decode** a message from the user.
+However, our code already facilitates this functionality.
+As mentioned in "Caesar Cipher Explanation", to decode an encoded message we can apply the opposite shift amount.
+In this sense, our code can both encode and decode ciphered text.
+
+This solution will not accept anything that is not in the alphabet. So numbers, or symbols will break this code.
+In order for the solution to accept numbers and symbols we must check if the letter is in the alphabet and if not 
+then add it to `new_text` without any processing done to it. Example below.
+```python
+new_text = EMPTY STRING
+FOR EACH letter IN text
+    IF letter IN alphabet THEN
+        index = INDEX OF letter IN alphabet
+        index = index + shift_amount
+        index = index MOD 26
+        new_text = new_text + alphabet[index]
+    ELSE THEN
+        new_text = new_text + letter
+END
+
+OUTPUT new_text
+```