Lectures/Day_1/04_Functions/Functions.ipynb

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    "![NASA](http://www.nasa.gov/sites/all/themes/custom/nasatwo/images/nasa-logo.svg)\n",
    "\n",
    "<center><h1><font size=\"+3\">Spring 2017 Python Training</font></h1></center>\n",
    "\n",
    "---\n",
    "\n",
    "<center><h4>Langley Research Center - April 5, 2017</h4></center>"
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    "# Functions\n",
    "\n",
    "---\n",
    "\n",
    "```python\n",
    "def function_name(arguments):\n",
    "    # Python code\n",
    "\n",
    "    return object\n",
    "```"
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    "# Why have functions?\n",
    "\n",
    "---\n",
    "\n",
    "Functions allow us to reuse code many times repeatedly, or, more importantly, across different situations. Let's see this second capability in an example:"
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    "def my_function(x):\n",
    "    print(x**2)\n",
    "\n",
    "\n",
    "a = 5\n",
    "b = 'a string '\n",
    "\n",
    "my_function(a)\n",
    "my_function(b)"
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    "Functions allow us to reuse code:"
   ]
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    "def f(x):\n",
    "    # note the use of a return statement\n",
    "    return x * x\n",
    "\n",
    "print(f(3))\n",
    "print(f(3) + f(4))\n",
    "print(f(f(f(f(f(2))))))"
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    "# Arguments\n",
    "\n",
    "---\n",
    "\n",
    "Functions allow the following types of arguments between the `()`'s:\n",
    "\n",
    "* No arguments\n",
    "* Positional Arguments - order sensitive\n",
    "* Keyword Arguments - named variables (can have default values)\n",
    "* `*args` - a tuple of variable length\n",
    "* `**kwargs` - a dictionary of keyword arguments"
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    "# no arguments (useful for grouping codes)\n",
    "def driver():\n",
    "    # get user input\n",
    "    # check user input\n",
    "    # use input to perform specific operations\n",
    "    # any output\n",
    "    # checks or summaries\n",
    "    # exit\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    driver()"
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    "# positional arguments (expect specific variables)\n",
    "def sum(x, y):\n",
    "    return x + y\n",
    "\n",
    "print(sum(4, 248))"
   ]
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    "# keyword arguments (with defaults usually; variable length (like reading a file))\n",
    "def student_title(fname='Bob', lname='Brown'):\n",
    "    print('{:<10}, {:>20}'.format(fname.capitalize(), lname.capitalize()))\n",
    "\n",
    "student_title(lname='Smith')"
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    "# A small note about defaults\n",
    "\n",
    "---\n",
    "\n",
    "```python\n",
    "def f(x=1):\n",
    "    return x**2\n",
    "\n",
    "print(f())\n",
    "print(f(5))\n",
    "print(f(x=27))\n",
    "```"
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   "source": [
    "# In-Class Exercise\n",
    "\n",
    "Write a function that lists all files with a certain extension in the current directory. (__Hint:__ Use the `glob` package.)\n",
    "\n",
    "How might you extend this function to be useful to you and your projects?"
   ]
  }
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