Harmonise indentation

Parts of these tutorials were indented with tabs, and others with 4
spaces.  This conforms them all to 4 spaces.

Author: danielquinn

python/lesson2/tutorial.md

@@ -14,7 +14,7 @@ it a name then set its value.
 
 Now in the REPL type:
 
-	>>> year = 2016
+    >>> year = 2016
 
 In this example you have now stored the value `2016` into the variable `year`.
 See what happens next when you type `year' into the REPL. Does it show it back
@@ -30,9 +30,9 @@ variables with the maths operations we learnt in the previous tutorial.
 
 Now in the REPL type the following:
 
-	>>> revenue = 1000
-	>>> costs = 200
-	>>> profit = revenue - costs
+    >>> revenue = 1000
+    >>> costs = 200
+    >>> profit = revenue - costs
 
 Now type `profit` to see the results of this calculation. 
 
@@ -49,22 +49,22 @@ strings.
 
 Now in the REPL type:
 
-	>>> name = 'codebar'
-	>>> url = "codebar.io"
+    >>> name = 'codebar'
+    >>> url = "codebar.io"
 
 Now type `name` and `url` to see these strings shown back to you. As you can
 see Python allows both single and double quotes to denote a string variable.
 Double quotes are required if there is going to be an apostrophe in the string.
 
 For example:
 
-	message = "I'm a string"
+    message = "I'm a string"
 
 Sometimes you will need to use an apostrophe within a single quote, on
 occasions like this it is recommended to use "string escaping". This would look
 like:
 
-	message ='I\'m a string'
+    message ='I\'m a string'
 
 Try storing a string within a variable without quotes, see what happens?
 Numbers do not require quotation marks, whereas they are mandatory for storing
@@ -122,20 +122,20 @@ command. Let's create a variable in which to store the user input.
 
 Now type this into your REPL: 
 
-	>>> lucky_number = input("What is your lucky number? ")
+    >>> lucky_number = input("What is your lucky number? ")
 
 Type back your answer after it asks you.
 
 Now in the REPL type:
 
-	>>> food = input("What is your favourite food? ")
+    >>> food = input("What is your favourite food? ")
 
 Now we are going to put your response into another variable.
 
 Now try:
 
-	>>> my_name = input("What is your name? ")
-	>>> greeting = "Hello " + my_name
+    >>> my_name = input("What is your name? ")
+    >>> greeting = "Hello " + my_name
 
 Then type `greeting` into your REPL to receive your message. 
 

python/lesson4/tutorial.md

@@ -13,16 +13,16 @@ later to run these statements. Python comes with plenty of functions already
 built in that you can use to perform common tasks. One example should be
 something you're already familiar with:
 
-	>>> print("This is a function")
-	This is a function
-	
+    >>> print("This is a function")
+    This is a function
+    
 It is also possible to store the output of a function in a variable for future
 use. Let's try this with the built in function `len()`, which will provide us
 with the length of a string:
 
-	>>> length_of_my_string = len("This is my string")
-	>>> print(length_of_my_string)
-	17
+    >>> length_of_my_string = len("This is my string")
+    >>> print(length_of_my_string)
+    17
 
 The function `len()` takes one *argument*: the string it's measuring, and it
 returns an *integer*: the length of the string.  Here, we're storing the output