02. Numpy/Python structures (additionally).ipynb

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   "source": [
    "# Ещё немного о структурах данных в Python\n",
    "\n",
    "## Попов Артём, кафедра ММП ВМК МГУ\n",
    "\n",
    "О чём можно узнать из этого ноутбука:\n",
    "\n",
    "* конструкция enumerate\n",
    "* использования lambda функций при работе со списками\n",
    "* форматирование строк"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## enumerate"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "С помощью enumerate можно итерироваться по элементам списка, зная их индекс:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0 Маша\n",
      "1 Петя\n",
      "2 Вася\n"
     ]
    }
   ],
   "source": [
    "for i, x in enumerate(['Маша', 'Петя', 'Вася']):\n",
    "    print(i, x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "140364498558096 140364498558096\n",
      "140364498202672 140364498202672\n",
      "140364498202760 140364498202760\n"
     ]
    }
   ],
   "source": [
    "l = ['Маша', 'Петя', 'Вася']\n",
    "for i, x in enumerate(l):\n",
    "    print(id(l[i]), id(x))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## lambda-функции\n",
    "\n",
    "Механизм создания безымянных функций:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<function __main__.<lambda>>"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "lambda x: x ** 2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "4"
      ]
     },
     "execution_count": 4,
     "metadata": {},
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   ],
   "source": [
    "f = lambda x: x ** 2\n",
    "f(2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Например, такие функции можно использовать в функции sorted."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 2, 3, 4, 4, 6, 9]"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "l = [0, 9, 2, 4, 6,4, 2, 1, 3]\n",
    "sorted(l)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[9, 6, 4, 4, 3, 2, 2, 1, 0]"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sorted(l, reverse=True)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "l = [(1, 0), (1, 1), (1, 2), (0, 2), (0, 2), (0, 3), (2, 1)]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[(0, 2), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (2, 1)]"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# по умолчанию сортируется по первому элементу кортежей\n",
    "sorted(l)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[(1, 0), (1, 1), (2, 1), (1, 2), (0, 2), (0, 2), (0, 3)]"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# сортируется по второму элементу\n",
    "sorted(l, key=lambda x: x[1])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Форматирование строк"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Метод format можно использовать для форматирования строк.\n",
    "\n",
    "Можно задавать форматирование с помощью номеров аргументов:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "s = '{0}, {1} or {2}, what will i choose?'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'study, life or work, what will i choose?'"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s.format('study', 'life', 'work')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Можно делать именованные аргументы:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "s = '{good}, {bad} or {middle}, what will i choose?'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'study, work or life, what will i choose?'"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s.format(good='study', middle='life', bad='work')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Есть специальные приёмы фоматирования. Можно задать ширину поля и выравнивание по левому краю:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "from math import pi"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'pi is                                                                                    3.141592653589793'"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s = 'pi is {0:>100}'\n",
    "s.format(pi)"
   ]
  }
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