09_python_variable_scopes.ipynb

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   "source": [
    "# Python variables scope"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Global Variables\n",
    "Variable declared outside of the function or in global scope is known as global variable. This means, global variable can be accessed inside or outside of the function."
   ]
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   "cell_type": "code",
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   "metadata": {},
   "outputs": [
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     "text": [
      "('x inside :', 'global')\n",
      "('x outside:', 'global')\n"
     ]
    }
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   "source": [
    "x = \"global\"\n",
    "\n",
    "def foo():\n",
    "    print(\"x inside :\", x)\n",
    "\n",
    "foo()\n",
    "print(\"x outside:\", x)"
   ]
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   "source": [
    "What if you want to change value of x inside a function?"
   ]
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   "source": [
    "x = \"global\"\n",
    "\n",
    "def foo():\n",
    "    x = x * 2\n",
    "    print(x)\n",
    "foo() # UnboundLocalError: local variable 'x' referenced before assignment"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Local Variables\n",
    "A variable declared inside the function's body or in the local scope is known as local variable."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def foo():\n",
    "    y = \"local\"\n",
    "\n",
    "foo()\n",
    "print(y) # NameError: name 'y' is not defined"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Using Global and Local variables in same code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
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     "text": [
      "globalglobal\n",
      "local\n"
     ]
    }
   ],
   "source": [
    "x = \"global\"\n",
    "\n",
    "def foo():\n",
    "    global x\n",
    "    y = \"local\"\n",
    "    x = x * 2\n",
    "    print(x)\n",
    "    print(y)\n",
    "    \n",
    "foo()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Global variable and Local variable with same name"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = 5\n",
    "\n",
    "def foo():\n",
    "    x = 10\n",
    "    print(\"local x:\", x)\n",
    "\n",
    "foo()\n",
    "print(\"global x:\", x)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Nonlocal Variables\n",
    "Nonlocal variable are used in nested function whose local scope is not defined. This means, the variable can be neither in the local nor the global scope."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "invalid syntax (<ipython-input-1-7b08575a07db>, line 5)",
     "output_type": "error",
     "traceback": [
      "\u001b[0;36m  File \u001b[0;32m\"<ipython-input-1-7b08575a07db>\"\u001b[0;36m, line \u001b[0;32m5\u001b[0m\n\u001b[0;31m    nonlocal x\u001b[0m\n\u001b[0m             ^\u001b[0m\n\u001b[0;31mSyntaxError\u001b[0m\u001b[0;31m:\u001b[0m invalid syntax\n"
     ]
    }
   ],
   "source": [
    "def outer():\n",
    "    x = \"local\"\n",
    "    \n",
    "    def inner():\n",
    "        nonlocal x\n",
    "        x = \"nonlocal\"\n",
    "        print(\"inner:\", x)\n",
    "    \n",
    "    inner()\n",
    "    print(\"outer:\", x)\n",
    "\n",
    "outer()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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