Number_of_weekdays_in_month.ipynb

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   "source": [
    "If I were to pick the 5th Wednesday of each month, how screwy would our schedule be?"
   ]
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    "import calendar\n",
    "\n",
    "from itertools import islice\n",
    "from collections import defaultdict\n",
    "\n",
    "def itermonthday2_trunc(year, month):\n",
    "    cal = calendar.Calendar()\n",
    "    for (date, wkday) in cal.itermonthdays2(year, month):\n",
    "        if date > 0:\n",
    "            yield (date, wkday)\n",
    "\n",
    "def weekdays_for_month(year, month):\n",
    "    wkdays = defaultdict(list)\n",
    "    for (date, wkday) in itermonthday2_trunc(year, month):\n",
    "        wkdays[wkday].append(date)\n",
    "        \n",
    "    return wkdays"
   ]
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   "cell_type": "code",
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     "data": {
      "text/plain": [
       "defaultdict(list,\n",
       "            {0: [1, 8, 15, 22, 29],\n",
       "             1: [2, 9, 16, 23, 30],\n",
       "             2: [3, 10, 17, 24, 31],\n",
       "             3: [4, 11, 18, 25],\n",
       "             4: [5, 12, 19, 26],\n",
       "             5: [6, 13, 20, 27],\n",
       "             6: [7, 14, 21, 28]})"
      ]
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     "execution_count": 2,
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   "source": [
    "weekdays_for_month(2018,10)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Let's just make use of `calendar.monthrange` instead"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
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    "collapsed": true
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   "outputs": [],
   "source": [
    "def nth_wkday_of_month(year, month, wkday, n):\n",
    "    (wkday0, lastdate) = calendar.monthrange(year,month)\n",
    "    \n",
    "    date = (wkday-wkday0) % 7 + (n-1)* 7 + 1\n",
    "    if date > lastdate:\n",
    "        return None\n",
    "    else:\n",
    "        return date\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "def year_month_iter(y0,m0):\n",
    "    \"\"\"\n",
    "    convenience iterator for march through the months\n",
    "    allow for modulo\n",
    "    \"\"\"\n",
    "    m1 = (m0 - 1)\n",
    "    \n",
    "    while True:\n",
    "        y = y0 + m1 // 12\n",
    "        m = m1 % 12 + 1\n",
    "    \n",
    "        yield(y,m)\n",
    "        \n",
    "        m1 += 1\n",
    "    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
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     "text": [
      "2019/1/30\n",
      "2019/5/29\n",
      "2019/7/31\n",
      "2019/10/30\n",
      "2020/1/29\n",
      "2020/4/29\n",
      "2020/7/29\n",
      "2020/9/30\n",
      "2020/12/30\n",
      "2021/3/31\n",
      "2021/6/30\n",
      "2021/9/29\n",
      "2021/12/29\n",
      "2022/3/30\n",
      "2022/6/29\n",
      "2022/8/31\n",
      "2022/11/30\n",
      "2023/3/29\n",
      "2023/5/31\n",
      "2023/8/30\n",
      "2023/11/29\n",
      "2024/1/31\n",
      "2024/5/29\n",
      "2024/7/31\n",
      "2024/10/30\n",
      "2025/1/29\n",
      "2025/4/30\n",
      "2025/7/30\n",
      "2025/10/29\n",
      "2025/12/31\n",
      "2026/4/29\n",
      "2026/7/29\n",
      "2026/9/30\n",
      "2026/12/30\n",
      "2027/3/31\n",
      "2027/6/30\n",
      "2027/9/29\n",
      "2027/12/29\n",
      "2028/3/29\n",
      "2028/5/31\n",
      "2028/8/30\n",
      "2028/11/29\n"
     ]
    }
   ],
   "source": [
    "# 5th wednesdays of the month\n",
    "\n",
    "\n",
    "for (year, month) in islice(year_month_iter(2019,1),120):\n",
    "    # looking for 5th wednesdays\n",
    "    date = nth_wkday_of_month(year, month, 2, 5)\n",
    "    if date is not None:\n",
    "        print (\"{}/{}/{}\".format(year, month, date))"
   ]
  },
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