{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Stack:\n",
    "\n",
    "    # Python list implementation of stacks\n",
    "\n",
    "    def __init__(self):\n",
    "    # construct an empty stack\n",
    "        self._data = []\n",
    "\n",
    "    def __str__(self):\n",
    "    # string representation of internal state of the stack\n",
    "        return \"TOP: \"+ str(self._data)\n",
    "        \n",
    "    def __len__(self):\n",
    "    # returns number of items in stack\n",
    "        return len(self._data)\n",
    "\n",
    "    def is_empty(self):\n",
    "    # returns True if stack is empty and False otherwise\n",
    "        return self._data == []\n",
    "\n",
    "    def top(self):\n",
    "    # returns top item of stack it stack is not empty; otherwise returns None\n",
    "        return self._data[0]\n",
    "\n",
    "    def pop(self):\n",
    "    # similar to top, except this also deletes top item from stack.\n",
    "        x = self._data[0]\n",
    "        self._data.remove(x)\n",
    "        return x\n",
    "        \n",
    "    def push(self,e):\n",
    "    # puts new item e on top of stack\n",
    "        self._data = [e] + self._data\n",
    "    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [],
   "source": [
    "s1 = Stack()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [],
   "source": [
    "s1.push(5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "TOP: [5]\n"
     ]
    }
   ],
   "source": [
    "print(s1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [],
   "source": [
    "s1.push(8)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "TOP: [8, 5]\n"
     ]
    }
   ],
   "source": [
    "print(s1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [],
   "source": [
    "s1.push(3)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "TOP: [3, 8, 5]\n"
     ]
    }
   ],
   "source": [
    "print(s1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3\n"
     ]
    }
   ],
   "source": [
    "print(s1.pop())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "TOP: [8, 5]\n"
     ]
    }
   ],
   "source": [
    "print(s1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [],
   "source": [
    "s = [1,2,3,4,5,6,7,8,9,10]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "4"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s[3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[4, 5, 6]"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s[3:6]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s[0]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [],
   "source": [
    "s.remove(s[0])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[2, 3, 4, 5, 6, 7, 8, 9, 10]\n"
     ]
    }
   ],
   "source": [
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "9"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "len(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [],
   "source": [
    "s = \"Sunderraman\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "6"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s.find('ram')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [],
   "source": [
    "s = [1,2,3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'[1, 2, 3]'"
      ]
     },
     "execution_count": 24,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "str(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "input a string (q to quit): abc\n",
      "reverse of string: cba\n",
      "input a string (q to quit): this is a long sentence\n",
      "reverse of string: ecnetnes gnol a si siht\n",
      "input a string (q to quit):    hello     \n",
      "reverse of string: olleh\n",
      "input a string (q to quit): q\n"
     ]
    }
   ],
   "source": [
    "def main():\n",
    "    # implements the Reverse program\n",
    "    while True:\n",
    "        s = input(\"input a string (q to quit): \").strip()\n",
    "        if s == 'q':\n",
    "            break\n",
    "        st = Stack()\n",
    "        for c in s:\n",
    "            st.push(c)\n",
    "        t = \"\"\n",
    "        while True:\n",
    "            if st.is_empty():\n",
    "                break\n",
    "            t = t + st.pop()\n",
    "        print(\"reverse of string: \"+t)\n",
    "            \n",
    "\n",
    "main()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
 ],
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