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    "# Python Functions\n",
    "\n",
    "A function is reusable block of code that performs a single task and can be used repeatedly in programs.  In Python, a basic function can be declared as follows:\n",
    "\n",
    "``` python\n",
    "def addNumbers(a:int, b:int) -> int:\n",
    "    return a+b\n",
    "```\n",
    "\n",
    "The above example, the following items should be noted:\n",
    "\n",
    "- The `def` keyword declares the start of a function\n",
    "- The name of this function is `addNumbers`\n",
    "- The function accepts two arguments, `a` and `b`.\n",
    "\n",
    "   - Each argument can be labelled to show the expected data type (i.e. `a:int` shows that the `a` argument is expecting an `int`).\n",
    "   - The `-> int` declares what the function will `return` (see below).\n",
    "\n",
    "- Similar to other Python constructs, the declaration line ends with a colon (`:`).\n",
    "- In standard circumstances, a Python function will `return` a value\n",
    "\n",
    "Functions are useful for repeated actions.  A famous principle of software development is \"Don't Repeat Yourself\" (aka DRY code).  As an example, writing the same message to multiple users could be performed as follows:\n",
    "\n",
    "``` python\n",
    "user1 = \"Carl\"\n",
    "user2 = \"Jim\"\n",
    "user3 = \"Fred\"\n",
    "\n",
    "print(\"Greetings \" + user1 + \", welcome to this program.\")\n",
    "print(\"Greetings \" + user2 + \", welcome to this program.\")\n",
    "print(\"Greetings \" + user3 + \", welcome to this program.\")\n",
    "```\n",
    "\n",
    "Clearly, the same lines are being repeated over and over.  This could be re-written as a function:\n",
    "\n",
    "``` python\n",
    "def greet(user:str) -> str:\n",
    "    return \"Greetings \" + user + \", welcome to this program.\"\n",
    "\n",
    "user1 = \"Carl\"\n",
    "user2 = \"Jim\"\n",
    "user3 = \"Fred\"\n",
    "\n",
    "print(greet(user1))\n",
    "print(greet(user2))\n",
    "print(greet(user3))\n",
    "```\n",
    "\n",
    "Both of these examples will have the same output, but using the function will require less effort for the programmer and be much more robust and maintainable."
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