13-identity-operator.ipynb

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   "source": [
    "# Identity operator `is`"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
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     "slide_type": "fragment"
    }
   },
   "source": [
    "This operator is used to check if two variables point to the same location or the same object"
   ]
  },
  {
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   "execution_count": 2,
   "metadata": {
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   "outputs": [],
   "source": [
    "x = 10\n",
    "y = x\n",
    "z = 10"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
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     "data": {
      "text/plain": [
       "True"
      ]
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     "execution_count": 3,
     "metadata": {},
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   ],
   "source": [
    "x is y"
   ]
  },
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   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
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    {
     "data": {
      "text/plain": [
       "True"
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     "execution_count": 4,
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   ],
   "source": [
    "x is z"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### The `id(object)` function in python\n",
    "It can be used to find the location or identity of an object in python."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
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    "slideshow": {
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "id(x) = 1794980240\n",
      "id(y) = 1794980240\n",
      "id(z) = 1794980240\n"
     ]
    }
   ],
   "source": [
    "print('id(x) =', id(x))\n",
    "print('id(y) =', id(y))\n",
    "print('id(z) =', id(z))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can see here that all three variables have the same id, i.e. they point to the same location, which means they are essentially the same object."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
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     "slide_type": "slide"
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "x = 10\n",
      "y = 15\n"
     ]
    }
   ],
   "source": [
    "y = y + 5\n",
    "print('x =', x)\n",
    "print('y =', y)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "id(x) = 1794980240\n",
      "id(y) = 1794980320\n"
     ]
    }
   ],
   "source": [
    "print('id(x) =', id(x))\n",
    "print('id(y) =', id(y))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "x is y"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "As the value of `y` is changed, `y` points to another object."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "---"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
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   },
   "outputs": [],
   "source": [
    "a = 19230248029843234\n",
    "b = 19230248029843234"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a == b True\n",
      "a is b False\n",
      "id(a) = 18571296\n",
      "id(b) = 18571320\n"
     ]
    }
   ],
   "source": [
    "print('a == b', a == b)\n",
    "print('a is b', a is b)\n",
    "print('id(a) =', id(a))\n",
    "print('id(b) =', id(b))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "### Python caches integers in the range <font color=\"purple\">[-5, 256]</font>\n",
    "\n",
    "All variables storing a value within this range simply points to the already existing value in the python integer cache, hence reducing space usage and speeding up execution."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "---"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "outputs": [],
   "source": [
    "a = [1, 2, 3]\n",
    "b = [1, 2, 3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "scrolled": true,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a == b True\n",
      "a is b False\n",
      "id(a) = 18014160\n",
      "id(b) = 18012160\n"
     ]
    }
   ],
   "source": [
    "print('a == b', a == b)\n",
    "print('a is b', a is b)\n",
    "print('id(a) =', id(a))\n",
    "print('id(b) =', id(b))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Any other value that is outside the range of integers cached by python will produce different objects when assigned to different variables, even if they have the same value."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "---"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "a = [3, 4, 5]\n",
    "b = a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`b` points to the same object as `a`, `a` and `b` are not two different objects, they are two references to the same object. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a: [3, 4, 5, 6]\n",
      "b: [3, 4, 5, 6]\n"
     ]
    }
   ],
   "source": [
    "b.append(6)\n",
    "print('a:', a)\n",
    "print('b:', b)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a == b True\n",
      "a is b True\n",
      "id(a) = 98031136\n",
      "id(b) = 98031136\n"
     ]
    }
   ],
   "source": [
    "print('a == b', a == b)\n",
    "print('a is b', a is b)\n",
    "print('id(a) =', id(a))\n",
    "print('id(b) =', id(b))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "skip"
    }
   },
   "source": [
    "***"
   ]
  },
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   },
   "source": [
    "![questions.jpg](img/questions.jpg)"
   ]
  }
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