06. Timezone.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Timezone"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "from datetime import datetime, timezone, timedelta\n",
    "import pytz\n",
    "import pandas as pd\n",
    "import matplotlib.pyplot as plt\n",
    "import matplotlib.dates as dates"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Python 내장 패키지를 사용하면 utc timezone 을 설정할 수 있습니다."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.timezone.utc"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "timezone.utc"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2019, 1, 1, 0, 0)"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# timezone unawared datetime\n",
    "datetime(2019,1,1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2019, 1, 1, 0, 0, tzinfo=datetime.timezone.utc)"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# timezone awared datetime\n",
    "datetime(2019,1,1,tzinfo=timezone.utc) "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "그러나 utc 외 timezone 을 표시하기 어렵기 때문에 pytz 패키지를 사용합니다."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "datetime(2019,1,1,tzinfo=timezone.utc) == pytz.UTC.localize(datetime(2019,1,1))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 한국 표준시\n",
    "KST = pytz.timezone('Asia/Seoul')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "datetime(2019,1,1,tzinfo=timezone.utc) == KST.localize(datetime(2019,1,1))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [],
   "source": [
    "# timezone unawared datetime\n",
    "mydate = datetime(2019,1,1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2019, 1, 1, 0, 0)"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "mydate"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [],
   "source": [
    "# timezone awared datetime\n",
    "mydate_kst = KST.localize(mydate)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2019, 1, 1, 0, 0, tzinfo=<DstTzInfo 'Asia/Seoul' KST+9:00:00 STD>)"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "mydate_kst"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2018, 12, 31, 15, 0, tzinfo=<UTC>)"
      ]
     },
     "execution_count": 17,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# timezone conversion\n",
    "mydate_kst.astimezone(pytz.utc)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "mydate_kst.astimezone(pytz.utc) == mydate_kst"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Timezone formatting\n",
    "timezone awared datetime 을 문자열로 표시할 때도 timezone 정보를 포함시킬 수 있습니다."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'2019-01-01 00:00:00KST'"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# strftime.org 참조\n",
    "mydate_kst.strftime(\"%Y-%m-%d %H:%M:%S%Z\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'2018-12-31 15:00:00UTC'"
      ]
     },
     "execution_count": 20,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "mydate_kst.astimezone(pytz.utc).strftime(\"%Y-%m-%d %H:%M:%S%Z\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Current datetime"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [],
   "source": [
    "today = datetime.today()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**today** 메서드는 시스템에 설정된 환경정보에 따라 timezone 정보 없이 데이터를 리턴하므로 다른 환경의 다른 컴퓨터에서 같은 코드를 실행할 시 문제를 발생시킬 수 있습니다. 절대적인 값으로 현재 시각을 가져올 방법이 필요합니다. **utcnow** 함수는 UTC 기준의 현재 시각을 리턴합니다."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2019, 1, 31, 8, 40, 49, 276846)"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# utc 표준시 이지만 time unawared datetime 입니다.\n",
    "datetime.utcnow()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2019, 1, 31, 8, 42, 47, 131384, tzinfo=<DstTzInfo 'Asia/Seoul' KST+9:00:00 STD>)"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# time awared datetime 으로 만들어 사용\n",
    "datetime.utcnow().astimezone(KST)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 최근 금요일 날짜 리턴하는 함수 만들기"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "요일 가져오기"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2"
      ]
     },
     "execution_count": 29,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 요일 가져오기; 0:월, 1:화, ... , 6:일\n",
    "datetime(2019,1,23).weekday()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "3"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "today.weekday()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "시간차 정보 다루기"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.timedelta(seconds=32400)"
      ]
     },
     "execution_count": 31,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# UTC 시간과 KST 시간 차이는 9시간\n",
    "pytz.utc.localize(mydate) - KST.localize(mydate)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2019, 1, 1, 9, 0, tzinfo=<UTC>)"
      ]
     },
     "execution_count": 32,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# UTC 시간에 9시간을 더하기\n",
    "pytz.utc.localize(mydate) + timedelta(seconds=32400)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {},
   "outputs": [],
   "source": [
    "def last_friday():\n",
    "    today = KST.localize(datetime.today())\n",
    "    offset = 4 - today.weekday() % 4\n",
    "    aweekago = today - timedelta(weeks=1)\n",
    "    last_friday = aweekago + timedelta(days=offset)\n",
    "    return last_friday"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.datetime(2019, 1, 25, 17, 48, 32, 512183, tzinfo=<DstTzInfo 'Asia/Seoul' KST+9:00:00 STD>)"
      ]
     },
     "execution_count": 34,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "last_friday()"
   ]
  }
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