]
}
],
- "prompt_number": 7
+ "prompt_number": 1
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "Let's see how it works."
+ ]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
- "ls"
+ "import sightings\n",
+ "sightings.count_wolverines('big_animals.txt')"
],
"language": "python",
"metadata": {},
"outputs": [
{
- "output_type": "stream",
- "stream": "stdout",
+ "output_type": "pyout",
+ "prompt_number": 2,
"text": [
- "README.md instructor_notebook.ipynb\r\n",
- "animals.txt ipython_nose.py\r\n",
- "big_animals.txt macguffin_animals.txt\r\n",
- "dev_notes.md merida_animals.txt\r\n",
- "dingwall_animals.txt student_notebook.ipynb\r\n",
- "fergus_animals.txt\r\n"
+ "117"
]
}
],
- "prompt_number": 1
+ "prompt_number": 2
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "***\n",
+ "# Refactoring\n",
+ "***\n",
+ "\n",
+ "Look at `count_wolverines`. You'll notice that there's a lot going on within this function. It:\n",
+ "\n",
+ "* Opens a file\n",
+ "* Reads lines from a file\n",
+ "* Closes the file\n",
+ "* Parses the string data from the file into usable data types\n",
+ "* Filters out records specific to a single animal\n",
+ "* Sums up a specific field contained within that set of filtered records\n",
+ "\n",
+ "You can imagine that we might want to do many things with data from the sightings file. For one, we want to average the number of sightings for a particular animal. Perhaps we want to count up the number of unique animals seen in a data set. Perhaps we want to figure out which days of the year have the most elk sightings. It's easy to see how we could modify the `count_wolverines` function above to achieve all of these goals, but if we simply replicated that entire function a half-dozen times, we would be repeating the code that opens the file and reads and splits the lines a half-dozen times, too.\n",
+ "\n",
+ "One approach to reducing this duplication is to *decompose* the function above into several separate functions, each with a single, small, well-defined responsibility (remember our list of good function criteria from the Intro session). This is often known as [refactoring](http://en.wikipedia.org/wiki/Code_refactoring). The goal is to rearrange code to make it easier to read, maintain, and reuse while preserving the existing functionality.\n",
+ "\n",
+ "We are going to *extract* a new function from `count_wolverines`.\n",
+ "\n",
+ "Create a new function called `read_sightings_from_file`. The function should:\n",
+ "\n",
+ "* Accept a sightings filename as a parameter\n",
+ "* Open the file\n",
+ "* Read the file's lines\n",
+ "* Split the lines\n",
+ "* Store each column of each line in a list dedicated to holding that type of data (i.e. dates, times, animals, counts)\n",
+ "* Return the lists\n",
+ "\n",
+ "For example, given the following file:"
+ ]
},
{
"cell_type": "code",
]
}
],
- "prompt_number": 2
+ "prompt_number": 3
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "your function would return:\n",
+ "\n",
+ " (['2011-04-22', '2011-04-23', ...], ['21:06', '14:12', ...], ['Grizzly', 'Elk', ...], [36, 25, ...])\n",
+ "\n",
+ "Keep in mind that most of this functionality is already implemented in `count_wolverines`, so you can copy liberally from that function."
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "## Results\n",
+ "\n",
+ "When you are done, the file `sightings.py` should look something like this (run the cell below to create it if you need help)."
+ ]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
- "def read_file(ifile):\n",
- " open_file = open(ifile, 'r')\n",
- " \n",
- " time = []\n",
- " date = []\n",
- " animal = []\n",
- " count = []\n",
+ "%%file sightings.py\n",
+ "def read_sightings_from_file(filename):\n",
+ " ''' Given a plain text file containing animal sighting data in the form\n",
+ " date time animal count\n",
+ " returns four lists, each containing the data from one column.'''\n",
" \n",
- " for iline in open_file:\n",
- " s = iline.split()\n",
- " date.append(s[0])\n",
- " time.append(s[1])\n",
- " animal.append(s[2])\n",
- " count.append(int(s[3]))\n",
+ " animal_file = open(filename, 'r')\n",
+ " animal_file_lines = animal_file.readlines()\n",
+ " animal_file.close()\n",
" \n",
- " open_file.close()\n",
+ " dates = []\n",
+ " times = []\n",
+ " animals = []\n",
+ " counts = []\n",
" \n",
- " return date, time, animal, count"
+ " for line in animal_file_lines:\n",
+ " date, time, animal, count_string = line.split()\n",
+ " dates.append(date)\n",
+ " times.append(time)\n",
+ " animals.append(animal)\n",
+ " counts.append(int(count_string))\n",
+ "\n",
+ " return dates, times, animals, counts\n",
+ "\n",
+ "def count_wolverines(filename):\n",
+ " '''Given a plain text file containing animal sighting data in the form \n",
+ " date time animal count\n",
+ " returns the total count of wolverines sighted.'''\n",
+ " animal_file = open(filename, 'r')\n",
+ " animal_file_lines = animal_file.readlines()\n",
+ " animal_file.close()\n",
+ "\n",
+ " total_count = 0\n",
+ " for line in animal_file_lines:\n",
+ " date, time, animal, count_string = line.split()\n",
+ " if animal == 'Wolverine':\n",
+ " total_count = total_count + int(count_string)\n",
+ " return total_count"
],
"language": "python",
"metadata": {},
- "outputs": [],
- "prompt_number": 15
+ "outputs": [
+ {
+ "output_type": "stream",
+ "stream": "stdout",
+ "text": [
+ "Overwriting sightings.py\n"
+ ]
+ }
+ ],
+ "prompt_number": 12
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "Let's see how it works."
+ ]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
- "read_file('animals.txt')"
+ "cat animals.txt"
+ ],
+ "language": "python",
+ "metadata": {},
+ "outputs": [
+ {
+ "output_type": "stream",
+ "stream": "stdout",
+ "text": [
+ "2011-04-22 21:06 Grizzly 36\r\n",
+ "2011-04-23 14:12 Elk 25\r\n",
+ "2011-04-23 10:24 Elk 26\r\n",
+ "2011-04-23 20:08 Wolverine 31\r\n",
+ "2011-04-23 18:46 Muskox 20\r\n"
+ ]
+ }
+ ],
+ "prompt_number": 13
+ },
+ {
+ "cell_type": "code",
+ "collapsed": false,
+ "input": [
+ "reload(sightings)\n",
+ "sightings.read_sightings_from_file('animals.txt')"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "pyout",
- "prompt_number": 7,
+ "prompt_number": 14,
"text": [
"(['2011-04-22', '2011-04-23', '2011-04-23', '2011-04-23', '2011-04-23'],\n",
" ['21:06', '14:12', '10:24', '20:08', '18:46'],\n",
]
}
],
- "prompt_number": 7
+ "prompt_number": 14
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "***\n",
+ "**Aside: Updating `count_wolverines`**\n",
+ "\n",
+ "Now that we have extracted the `read_sightings_from_file` function, we could remove the duplicated code from `count_wolverines`, which would simplify that function a bit."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "collapsed": false,
+ "input": [
+ "%%file sightings.py\n",
+ "def read_sightings_from_file(filename):\n",
+ " ''' Given a plain text file containing animal sighting data in the form\n",
+ " date time animal count\n",
+ " returns four lists, each containing the data from one column.'''\n",
+ " \n",
+ " animal_file = open(filename, 'r')\n",
+ " animal_file_lines = animal_file.readlines()\n",
+ " animal_file.close()\n",
+ " \n",
+ " dates = []\n",
+ " times = []\n",
+ " animals = []\n",
+ " counts = []\n",
+ " \n",
+ " for line in animal_file_lines:\n",
+ " date, time, animal, count_string = line.split()\n",
+ " dates.append(date)\n",
+ " times.append(time)\n",
+ " animals.append(animal)\n",
+ " counts.append(int(count_string))\n",
+ " \n",
+ " return dates, times, animals, counts\n",
+ "\n",
+ "def count_wolverines(filename):\n",
+ " '''Given a plain text file containing animal sighting data in the form \n",
+ " date time animal count\n",
+ " returns the total count of wolverines sighted.'''\n",
+ " \n",
+ " dates, times, animals, counts = read_sightings_from_file(filename)\n",
+ " \n",
+ " total_count = 0\n",
+ " \n",
+ " for animal, count in zip(animals, counts):\n",
+ " if animal == 'Wolverine':\n",
+ " total_count = total_count + count\n",
+ " return total_count"
+ ],
+ "language": "python",
+ "metadata": {},
+ "outputs": [
+ {
+ "output_type": "stream",
+ "stream": "stdout",
+ "text": [
+ "Overwriting sightings.py\n"
+ ]
+ }
+ ],
+ "prompt_number": 15
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "Does it work?"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "collapsed": false,
+ "input": [
+ "reload(sightings)\n",
+ "sightings.count_wolverines('big_animals.txt')"
+ ],
+ "language": "python",
+ "metadata": {},
+ "outputs": [
+ {
+ "output_type": "pyout",
+ "prompt_number": 16,
+ "text": [
+ "117"
+ ]
+ }
+ ],
+ "prompt_number": 16
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "***"
+ ]
},
{
"cell_type": "code",
projects / swc-testing-nose.git / commitdiff