Week-08.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# More booleans"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Our tl;dr summary from last week:\n",
    "\n",
    "* `if`: required, only once, and always your first statement. Put a conditional check after.\n",
    "* `elif`: optional, may appear many times, and must be directly after an `if` statement. On the same block level as your `if` statement.\n",
    "* `else`: optional, may appear once, and only as your last statement in the if block.  On the same block level as your if statement."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This week, let's talk more about designing complex structures and doing test driven development.\n",
    "\n",
    "So you've got a complex problem, and remember that you should start from the broadest strokes and work your way inside. When there are many rules and threads, it can be helpful to predetermine answers and use that to test your progress."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "PE11: A year is a leap year if it is divisible by 4, unless it is a century year that is not divisible by 400.  (1800 and 1900 are not leap years while 1600 and 2000 are).   Write a program that calculates whether a year is a leap year.\n",
    "\n",
    "* What's the input?\n",
    "    * a year, thus an integer\n",
    "* What's the output?\n",
    "    * It doesn't specify, but this a yes/no question, thus boolean\n",
    "    * so return either `True` or `False`\n",
    "    \n",
    "Let's start unpacking these rules:\n",
    "\n",
    "* divisble by 4\n",
    "    * `year % 4 == 0`\n",
    "* century year not divisible by 4\n",
    "    * `year % 100 == 0` and `year % 400 != 0`\n",
    "    \n",
    "Let's start setting up this function, but better yet, let's set up a battery of tests for oursevles."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "I just googled for a list of leap years.  OO, check this out:  https://en.wikipedia.org/wiki/Leap_year#Algorithm\n",
    "\n",
    "* if (year is not divisible by 4) then (it is a common year)\n",
    "* else if (year is not divisible by 100) then (it is a leap year)\n",
    "* else if (year is not divisible by 400) then (it is a common year)\n",
    "* else (it is a leap year)\n",
    "\n",
    "We are also in a position where we can seed ourselves some test cases where we know what the answer should be.  "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "list_o_years = [1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, \n",
    "                1936, 1940, 1944, 1948, 1952, 1956, 1960, 1964, \n",
    "                1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, \n",
    "                2000, 2004, 2008, 2012, 2016, 2020]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1904 is False1908 is False1912 is False1916 is False1920 is False1924 is False1928 is False1932 is False1936 is False1940 is False1944 is False1948 is False1952 is False1956 is False1960 is False1964 is False1968 is False1972 is False1976 is False1980 is False1984 is False1988 is False1992 is False1996 is False2000 is False2004 is False2008 is False2012 is False2016 is False2020 is False"
     ]
    }
   ],
   "source": [
    "# let's get a base\n",
    "\n",
    "\n",
    "def is_leap_year(year):\n",
    "    \"\"\"Return True if a year is a leap year\"\"\"\n",
    "    return False\n",
    "\n",
    "for year in list_o_years:\n",
    "    # we know all of these should be true, so let's \n",
    "    print(year, \"is\", is_leap_year(year), end = \"\") # no newlines for shortness"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1904 is False\n",
      "1908 is False\n",
      "1912 is False\n",
      "1916 is False\n",
      "1920 is False\n",
      "1924 is False\n",
      "1928 is False\n",
      "1932 is False\n",
      "1936 is False\n",
      "1940 is False\n"
     ]
    }
   ],
   "source": [
    "# starting to fill things out via the wikipedia algorithm\n",
    "\n",
    "def is_leap_year(year):\n",
    "    \"\"\"Return True if a year is a leap year\"\"\"\n",
    "    # if (year is not divisible by 4) then (it is a common year)\n",
    "    if year % 4 != 0:\n",
    "        return False\n",
    "    else:\n",
    "        return False\n",
    "\n",
    "for year in list_o_years[:10]: # let's start with a smaller group\n",
    "    # we know all of these should be true, so let's \n",
    "    print(year, \"is\", is_leap_year(year))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
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    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1904 is True\n",
      "1908 is True\n",
      "1912 is True\n",
      "1916 is True\n",
      "1920 is True\n",
      "1924 is True\n",
      "1928 is True\n",
      "1932 is True\n",
      "1936 is True\n",
      "1940 is True\n"
     ]
    }
   ],
   "source": [
    "# starting to fill things out via the wikipedia algorithm\n",
    "\n",
    "def is_leap_year(year):\n",
    "    \"\"\"Return True if a year is a leap year\"\"\"\n",
    "    # if (year is not divisible by 4) then (it is a common year)\n",
    "    if year % 4 != 0:\n",
    "        return False\n",
    "    # else if (year is not divisible by 100) then (it is a leap year)\n",
    "    elif year % 100 != 0:\n",
    "        return True\n",
    "    else:\n",
    "        return False\n",
    "\n",
    "for year in list_o_years[:10]: # let's start with a smaller group\n",
    "    # we know all of these should be true, so let's \n",
    "    print(year, \"is\", is_leap_year(year))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Oh look! All of our years are coming up as True, which is great.  Let's check the rest now."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
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    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1904 is True\n",
      "1908 is True\n",
      "1912 is True\n",
      "1916 is True\n",
      "1920 is True\n",
      "1924 is True\n",
      "1928 is True\n",
      "1932 is True\n",
      "1936 is True\n",
      "1940 is True\n",
      "1944 is True\n",
      "1948 is True\n",
      "1952 is True\n",
      "1956 is True\n",
      "1960 is True\n",
      "1964 is True\n",
      "1968 is True\n",
      "1972 is True\n",
      "1976 is True\n",
      "1980 is True\n",
      "1984 is True\n",
      "1988 is True\n",
      "1992 is True\n",
      "1996 is True\n",
      "2000 is False\n",
      "2004 is True\n",
      "2008 is True\n",
      "2012 is True\n",
      "2016 is True\n",
      "2020 is True\n"
     ]
    }
   ],
   "source": [
    "for year in list_o_years: # let's start with a smaller group\n",
    "    # we know all of these should be true, so let's \n",
    "    print(year, \"is\", is_leap_year(year))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "That one failure!!!! Let's be sure and finish adding in the algorithm."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1904 is True\n",
      "1908 is True\n",
      "1912 is True\n",
      "1916 is True\n",
      "1920 is True\n",
      "1924 is True\n",
      "1928 is True\n",
      "1932 is True\n",
      "1936 is True\n",
      "1940 is True\n",
      "1944 is True\n",
      "1948 is True\n",
      "1952 is True\n",
      "1956 is True\n",
      "1960 is True\n",
      "1964 is True\n",
      "1968 is True\n",
      "1972 is True\n",
      "1976 is True\n",
      "1980 is True\n",
      "1984 is True\n",
      "1988 is True\n",
      "1992 is True\n",
      "1996 is True\n",
      "2000 is True\n",
      "2004 is True\n",
      "2008 is True\n",
      "2012 is True\n",
      "2016 is True\n",
      "2020 is True\n"
     ]
    }
   ],
   "source": [
    "def is_leap_year(year):\n",
    "    \"\"\"Return True if a year is a leap year\"\"\"\n",
    "    # if (year is not divisible by 4) then (it is a common year)\n",
    "    if year % 4 != 0:\n",
    "        return False\n",
    "    # else if (year is not divisible by 100) then (it is a leap year)\n",
    "    elif year % 100 != 0:\n",
    "        return True\n",
    "    # else if (year is not divisible by 400) then (it is a common year)\n",
    "    elif year % 400 != 0:\n",
    "        return False\n",
    "    else:\n",
    "    # else (it is a leap year)\n",
    "        return True\n",
    "\n",
    "for year in list_o_years: # let's start with a smaller group\n",
    "    # we know all of these should be true, so let's \n",
    "    print(year, \"is\", is_leap_year(year))"
   ]
  },
  {
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   "execution_count": 19,
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    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1900 is NOT a leap year\n",
      "1901 is NOT a leap year\n",
      "1902 is NOT a leap year\n",
      "1903 is NOT a leap year\n",
      "1904 IS a leap year\n",
      "1905 is NOT a leap year\n",
      "1906 is NOT a leap year\n",
      "1907 is NOT a leap year\n",
      "1908 IS a leap year\n",
      "1909 is NOT a leap year\n",
      "1910 is NOT a leap year\n",
      "1911 is NOT a leap year\n",
      "1912 IS a leap year\n",
      "1913 is NOT a leap year\n",
      "1914 is NOT a leap year\n",
      "1915 is NOT a leap year\n",
      "1916 IS a leap year\n",
      "1917 is NOT a leap year\n",
      "1918 is NOT a leap year\n",
      "1919 is NOT a leap year\n",
      "1920 IS a leap year\n",
      "1921 is NOT a leap year\n",
      "1922 is NOT a leap year\n",
      "1923 is NOT a leap year\n",
      "1924 IS a leap year\n",
      "1925 is NOT a leap year\n",
      "1926 is NOT a leap year\n",
      "1927 is NOT a leap year\n",
      "1928 IS a leap year\n",
      "1929 is NOT a leap year\n",
      "1930 is NOT a leap year\n",
      "1931 is NOT a leap year\n",
      "1932 IS a leap year\n",
      "1933 is NOT a leap year\n",
      "1934 is NOT a leap year\n",
      "1935 is NOT a leap year\n",
      "1936 IS a leap year\n",
      "1937 is NOT a leap year\n",
      "1938 is NOT a leap year\n",
      "1939 is NOT a leap year\n",
      "1940 IS a leap year\n",
      "1941 is NOT a leap year\n",
      "1942 is NOT a leap year\n",
      "1943 is NOT a leap year\n",
      "1944 IS a leap year\n",
      "1945 is NOT a leap year\n",
      "1946 is NOT a leap year\n",
      "1947 is NOT a leap year\n",
      "1948 IS a leap year\n",
      "1949 is NOT a leap year\n",
      "1950 is NOT a leap year\n",
      "1951 is NOT a leap year\n",
      "1952 IS a leap year\n",
      "1953 is NOT a leap year\n",
      "1954 is NOT a leap year\n",
      "1955 is NOT a leap year\n",
      "1956 IS a leap year\n",
      "1957 is NOT a leap year\n",
      "1958 is NOT a leap year\n",
      "1959 is NOT a leap year\n",
      "1960 IS a leap year\n",
      "1961 is NOT a leap year\n",
      "1962 is NOT a leap year\n",
      "1963 is NOT a leap year\n",
      "1964 IS a leap year\n",
      "1965 is NOT a leap year\n",
      "1966 is NOT a leap year\n",
      "1967 is NOT a leap year\n",
      "1968 IS a leap year\n",
      "1969 is NOT a leap year\n",
      "1970 is NOT a leap year\n",
      "1971 is NOT a leap year\n",
      "1972 IS a leap year\n",
      "1973 is NOT a leap year\n",
      "1974 is NOT a leap year\n",
      "1975 is NOT a leap year\n",
      "1976 IS a leap year\n",
      "1977 is NOT a leap year\n",
      "1978 is NOT a leap year\n",
      "1979 is NOT a leap year\n",
      "1980 IS a leap year\n",
      "1981 is NOT a leap year\n",
      "1982 is NOT a leap year\n",
      "1983 is NOT a leap year\n",
      "1984 IS a leap year\n",
      "1985 is NOT a leap year\n",
      "1986 is NOT a leap year\n",
      "1987 is NOT a leap year\n",
      "1988 IS a leap year\n",
      "1989 is NOT a leap year\n",
      "1990 is NOT a leap year\n",
      "1991 is NOT a leap year\n",
      "1992 IS a leap year\n",
      "1993 is NOT a leap year\n",
      "1994 is NOT a leap year\n",
      "1995 is NOT a leap year\n",
      "1996 IS a leap year\n",
      "1997 is NOT a leap year\n",
      "1998 is NOT a leap year\n",
      "1999 is NOT a leap year\n",
      "2000 IS a leap year\n",
      "2001 is NOT a leap year\n",
      "2002 is NOT a leap year\n",
      "2003 is NOT a leap year\n",
      "2004 IS a leap year\n",
      "2005 is NOT a leap year\n",
      "2006 is NOT a leap year\n",
      "2007 is NOT a leap year\n",
      "2008 IS a leap year\n",
      "2009 is NOT a leap year\n",
      "2010 is NOT a leap year\n",
      "2011 is NOT a leap year\n",
      "2012 IS a leap year\n",
      "2013 is NOT a leap year\n",
      "2014 is NOT a leap year\n",
      "2015 is NOT a leap year\n",
      "2016 IS a leap year\n"
     ]
    }
   ],
   "source": [
    "for i in range(1900, 2017):\n",
    "    if is_leap_year(i):\n",
    "        print(i, \"IS a leap year\")\n",
    "    else:\n",
    "        print(i, \"is NOT a leap year\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {
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   "outputs": [
    {
     "name": "stdout",
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     "text": [
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n",
      "True\n"
     ]
    }
   ],
   "source": [
    "# more years from https://kalender-365.de/leap-years.php\n",
    "moreyears = [1804, 1808, 1812, 1816, 1820, 1824, 1828, 1832, 1836, 1840, 1844, \n",
    "             1848, 1852, 1856, 1860, 1864, 1868, 1872, 1876, 1880, 1884, 1888, \n",
    "             1892, 1896, 1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, \n",
    "             1940, 1944, 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, \n",
    "             1984, 1988, 1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020, 2024, \n",
    "             2028, 2032, 2036, 2040, 2044, 2048, 2052, 2056, 2060, 2064, 2068, \n",
    "             2072, 2076, 2080, 2084, 2088, 2092, 2096, 2104, 2108, 2112, 2116, \n",
    "             2120, 2124, 2128, 2132, 2136, 2140, 2144, 2148, 2152, 2156, 2160, \n",
    "             2164, 2168, 2172, 2176, 2180, 2184, 2188, 2192, 2196, 2204, 2208, \n",
    "             2212, 2216, 2220, 2224, 2228, 2232, 2236, 2240, 2244, 2248, 2252, \n",
    "             2256, 2260, 2264, 2268, 2272, 2276, 2280, 2284, 2288, 2292, 2296, \n",
    "             2304, 2308, 2312, 2316, 2320, 2324, 2328, 2332, 2336, 2340, 2344, \n",
    "             2348, 2352, 2356, 2360, 2364, 2368, 2372, 2376, 2380, 2384, 2388, \n",
    "             2392, 2396, 2400]\n",
    "\n",
    "for year in moreyears:\n",
    "    print(is_leap_year(year))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This is such a long list, it is hard to tell what is what.  We can use boolean testing in another way."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "for year in moreyears:\n",
    "    if not is_leap_year(year):\n",
    "        print(year)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Nothing came up!  That's to be expected if everything is working, but we can't see anything, so let's throw a kink in just to watch it work."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2017\n"
     ]
    }
   ],
   "source": [
    "moreyears.append(2017)\n",
    "\n",
    "for year in moreyears:\n",
    "    if not is_leap_year(year):\n",
    "        print(year)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Yup, it works!!!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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