Added Python explanation

Author: hrszpuk

Python/README.md

@@ -25,4 +25,47 @@ Read more:
 - [What is Checksum on a credit card?](https://www.sapling.com/7966257/checksum-credit-card)
 
 ### Python solution
+The Python solution is very similar to the pseudocode written in generalised solution of `README.md`.
+There are some Python specific functions/methods used which makes the code a lot more compact. 
 
+To begin with, we get the credit card number from the user and instantly convert it to a list.
+We then use `pop()`, a function that removes, and then returns, the last element of a list.
+We assign the return of `pop()`, the last number in `credit_card_number`, to `last_digit`.
+```python
+# Get input, define last_digit, and remove the 16th digit from the credit card.
+credit_card_number = list(input("Please enter the credit card number: "))
+last_digit = credit_card_number.pop()
+```
+
+Next is the meat of our code.
+We use `enumerate()` which, in Python, gives us both `i` the current index and `number` the current value at that index (e.g. the current number in `credit_card_number`).
+For each number in `credit_card_number` we do the following:
+1. Check if the index `i` of the `number` is even. If so we multiply that number by 2.
+2. We check if the current number is longer than 1 digit. If so we break up the number and add each digit together.
+3. Ensure every number in `credit_card_number` is an integer and not a string because later on we use `sum()` which doesn't like strings.
+```python
+# Make use of enumerate to get the index and value of each number in the credit card number.
+for i, number in enumerate(credit_card_number):
+    if i % 2 == 0:  # if the index is even (i.e. every other element)
+        credit_card_number[i] = int(number) * 2
+
+    # Check is the length of the number is more than a single digit.
+    if len(str(credit_card_number[i])) > 1:
+        # Break up the number into two digits and add them together
+        # Example: 12 := 1 + 2 = 3
+        x = str(credit_card_number[i])[0]
+        y = str(credit_card_number[i])[1]
+        credit_card_number[i] = int(x) + int(y)  # We replace the previous number with our new single digit one.
+
+    # Here we make sure every element is converted to an integer otherwise we have issues with sum() later on.
+    credit_card_number[i] = int(credit_card_number[i])
+```
+
+Finally, we check if the `credit_card_number` is valid.
+We add the sum of the `credit_card_number` and add the `last_digit` to it.
+We then check if the result is a multiple of 10 using `% 10 === 0`.
+```python
+# Add up all the numbers, add the 16th digit, then check if final number is a multiple of 10.
+is_valid = (sum(credit_card_number) + int(last_digit)) % 10 == 0
+print(f"Is credit card valid: {is_valid}")  # Output answer to user: True or False.
+```