copy or view

copy_or_view.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "import numpy as np\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Before:\n",
      " x = [0 1 2 3 4]\n",
      " y =    1\n",
      "\n",
      "After:\n",
      " x = [0 1 2 3 4]\n",
      " y =    2\n"
     ]
    }
   ],
   "source": [
    "# indexing by integer copies the value\n",
    "\n",
    "x = np.arange(5)\n",
    "\n",
    "# take second element\n",
    "y = x[1]\n",
    "\n",
    "print \"Before:\"\n",
    "print \" x =\", x\n",
    "print \" y =   \", y\n",
    "print \n",
    "\n",
    "# change y in place\n",
    "y+=1\n",
    "\n",
    "print \"After:\"\n",
    "print \" x =\", x\n",
    "print \" y =   \", y"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Before:\n",
      " x = [0 1 2 3 4]\n",
      " y = [0 1]\n",
      "\n",
      "After:\n",
      " x = [0 2 2 3 4]\n",
      " y = [0 2]\n",
      "\n"
     ]
    }
   ],
   "source": [
    "# indexing by a slice creates a view\n",
    "\n",
    "x = np.arange(5)\n",
    "\n",
    "# take first two elements\n",
    "y = x[:2]\n",
    "\n",
    "print \"Before:\"\n",
    "print \" x =\", x\n",
    "print \" y =\", y\n",
    "print \n",
    "\n",
    "# change second element of y in place\n",
    "y[1]+=1\n",
    "\n",
    "\n",
    "print \"After:\"\n",
    "print \" x =\", x\n",
    "print \" y =\", y\n",
    "print "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "\n"
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 2",
   "language": "python",
   "name": "python2"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 2
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython2",
   "version": "2.7.11"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 0
}