python-intro/exercises/ex13_writing_functions.ipynb

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    "# Exercise 13: Writing Functions"
   ]
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   "source": [
    "## Aim: Introduce writing and calling functions."
   ]
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    "### Issues covered:\n",
    "- Writing a simple function\n",
    "- Indenting code within a function\n",
    "- Sending arguments to functions\n",
    "- Calling functions\n",
    "- Checking arguments in functions"
   ]
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   "source": [
    "## 1. Let's write a simple function and use it"
   ]
  },
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   "source": [
    "Use the `def` function to define a function called `hello` to introduce yourself."
   ]
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   "source": [
    "Did the function return anything? If not, try running it!"
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   "source": [
    "## 2. Now let's write a function that takes an argument"
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   "source": [
    "Write a function which takes a number and doubles it."
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    "Test the function by calling it with an integer, then a float."
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    "What happens if you give it a string rather than a number?"
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    "What happens if you give it 2 numbers?"
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   "source": [
    "## 3. Let's take a look at what functions return"
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    "Why is the result of the following `None`? Can you fix it?\n",
    "```\n",
    "def print_time(hour, minute, second):\n",
    "    time_string = str(hour) + ':' + str(minute) + ':' + str(second)\n",
    "    print(time_string)\n",
    "\n",
    "result = print_time(11, 37, 59)\n",
    "print('result of call is:', result)\n",
    "```"
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    "Run the following and take a look at what it prints. Restructure it so that instead it prints `calling pressure is 22.5`.\n",
    "```\n",
    "def report(pressure):\n",
    "    print('pressure is', pressure)\n",
    "\n",
    "print('calling', report, 22.5)\n",
    "```"
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   "source": [
    "## 4. Let's write a function to use Pythagoras' Theorem, like in exercise 2."
   ]
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   "source": [
    "Define a function `calc_hypo` that takes two arguments, `a` and `b`. Inside the function, define a variable `hypo` equal to the length of the hypotenuse and return the value."
   ]
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   "source": [
    "Test out the function by calling it with the values `3` and `4`."
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   "source": [
    "Let's improve the function by adding some checks. Use `if` statements to print \"bad argument\" and return `None` if the argument type isn't `int` or `float`. "
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    "Call the function with different arguments to check that this is working."
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   "source": [
    "Add a second check to the function which prints \"Bad argument\" and returns `None` if a number equal to or less than zero is given."
   ]
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   "source": [
    "Test out the check you added."
   ]
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   "source": [
    "## 5. Extension Activity"
   ]
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   "source": [
    "1. Write a function which computes the average GDP for each file for a given country, continent and year."
   ]
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    "_Hint: You will need the following steps:_\n",
    "1. Create a function with the arguments country, continent, year.\n",
    "2. Read the csv file (use the continent variable in the filename to open any file - e.g. the file name should be /data/`continent`_gdp.csv).\n",
    "3. Use `.loc[ ]` to locate where the data for the country is.\n",
    "4. Work out the GDP decade using the year given (maybe using floor division `//`).\n",
    "5. Loop over the columns to find the one which starts with 'gdpPercap_`year`' (make use of `.index` and `.startswith()`).\n",
    "6. Try calling the function and see what it returns - if you call it for Canada, americas in 1952 your answer should be 11928.55559."
   ]
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