04. Methods and Functions/4.6 Nested Statements and Scope.ipynb

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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Nested Statements and Scope"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = 25\n",
    "\n",
    "def printer():\n",
    "    x = 50\n",
    "    return x"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "25\n"
     ]
    }
   ],
   "source": [
    "print(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "50\n"
     ]
    }
   ],
   "source": [
    "print(printer())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### LEGB Rule\n",
    "The order Python is going to look for variables in\n",
    "\n",
    "- `L` = Local - Names assigned in any way within a function (`def` or `lambda`)\n",
    "- `E` = Enclosing Function Locals - Names in the local scope of any and all enclosing functions (`def` or `lambda`), from inner to outer\n",
    "- `G` = Global (module) - Names assigned at the top-level of a module file, or declared globally in a `def` within the file\n",
    "- `B` = Built-in (Python) - Names preassigned in the buit-in names module: open, range, SyntaxError..."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Local"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<function __main__.<lambda>(num)>"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "lambda num:num**2 # num is a local variable"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello IM A LOCAL\n"
     ]
    }
   ],
   "source": [
    "# Global\n",
    "name = 'THIS IS A GLOBAL STRING'\n",
    "\n",
    "def greet():\n",
    "    # Enclosing\n",
    "    name = 'Sammy'\n",
    "    \n",
    "    def hello():\n",
    "        # Local\n",
    "        name = 'IM A LOCAL'\n",
    "        print('Hello ' + name)\n",
    "    hello()\n",
    "    \n",
    "greet()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Enclosing Function Locals"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello Sammy\n"
     ]
    }
   ],
   "source": [
    "# Global\n",
    "name = 'THIS IS A GLOBAL STRING'\n",
    "\n",
    "def greet():\n",
    "    # Enclosing\n",
    "    name = 'Sammy'\n",
    "    \n",
    "    def hello():\n",
    "        print('Hello ' + name)\n",
    "    hello()\n",
    "    \n",
    "greet()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello Sammy\n"
     ]
    }
   ],
   "source": [
    "greet()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Global"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello THIS IS A GLOBAL STRING\n"
     ]
    }
   ],
   "source": [
    "# Global\n",
    "name = 'THIS IS A GLOBAL STRING'\n",
    "\n",
    "def greet():\n",
    "    # Enclosing\n",
    "    # name = 'Sammy'\n",
    "    \n",
    "    def hello():\n",
    "        # Local\n",
    "        # name = 'IM A LOCAL'\n",
    "        print('Hello ' + name)\n",
    "    hello()\n",
    "    \n",
    "greet()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Built-in"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Help on built-in function len in module builtins:\n",
      "\n",
      "len(obj, /)\n",
      "    Return the number of items in a container.\n",
      "\n"
     ]
    }
   ],
   "source": [
    "help(len)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "If you can call `help()` on it and you get something back, it's built-in"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Global Keyword"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = 50"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [],
   "source": [
    "def func(x):\n",
    "    print(f'X is {x}')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "X is 50\n"
     ]
    }
   ],
   "source": [
    "func(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [],
   "source": [
    "def func(x):\n",
    "    print(f'X is {x}')\n",
    "    # Local Reassignment\n",
    "    x = 200\n",
    "    print(f'I just locally changed x to {x}')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "X is 50\n",
      "I just locally changed x to 200\n"
     ]
    }
   ],
   "source": [
    "func(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "50\n"
     ]
    }
   ],
   "source": [
    "print(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [],
   "source": [
    "def func():\n",
    "    global x # grab the x variable in the global namespace \n",
    "    print(f'X is {x}')\n",
    "    # Local Reassignment ON A GLOBAL VARIABLE\n",
    "    x = 200\n",
    "    print(f'I just locally changed GLOBAL x to {x}')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Anything that happens to `x` in the function will be applied to the global `x` vraiable"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "50"
      ]
     },
     "execution_count": 24,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "x"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "X is 50\n",
      "I just locally changed GLOBAL x to 200\n"
     ]
    }
   ],
   "source": [
    "func()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "200"
      ]
     },
     "execution_count": 26,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "x"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Better way instead of using `global` keyword:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [],
   "source": [
    "def func(x):\n",
    "    print(f'X is {x}')\n",
    "    # Local Reassignment\n",
    "    x = 200\n",
    "    print(f'I just locally changed x to {x}')\n",
    "    return x"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = 50"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "50"
      ]
     },
     "execution_count": 29,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "x"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "X is 50\n",
      "I just locally changed x to 200\n"
     ]
    }
   ],
   "source": [
    "x = func(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "200"
      ]
     },
     "execution_count": 31,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "x"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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