02_variables_autocomplete.ipynb

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   "source": [
    "# Variables & Auto-complete\n",
    "   1. [Variable Names](#Variable_Names)\n",
    "   2. [How to assign a value to a variable](#How_to_assign_a_value_to_a_variable)\n",
    "   3. [How to delete a variable](#How_to_delete_a_variable)\n",
    "   4. [How to use Jupyter notebook's Auto-Complete](#How_to_use_Jupyter_notebook's_Auto-Complete)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<a id=\"Variable_Names\"></a>\n",
    "### Variable Names\n",
    "A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for Python \n",
    "variables:                                                                                                                      \n",
    "A variable name must start with a letter or the underscore character\n",
    "\n",
    "A variable name cannot start with a number\n",
    "\n",
    "A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )\n",
    "\n",
    "Variable names are case-sensitive (age, Age and AGE are three different variables)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "myvar = \"John\"\n",
    "my_var = \"John\"\n",
    "_my_var = \"John\"\n",
    "myVar = \"John\"\n",
    "MYVAR = \"John\"\n",
    "myvar2 = \"John\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<a id=\"How_to_assign_a_value_to_a_variable\"></a>\n",
    "### Assigning Values to Variables"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "counter:  100\n",
      "name:  pooya\n",
      "height:  185.0\n"
     ]
    }
   ],
   "source": [
    "counter = 100\n",
    "name = 'pooya'\n",
    "height = 185.0\n",
    "\n",
    "\n",
    "print(\"counter: \", counter)\n",
    "print(\"name: \", name)\n",
    "print(\"height: \", height)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<a id=\"How_to_assign_a_value_to_a_variable\"></a>\n",
    "### Multiple Assignment"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 1 1\n"
     ]
    }
   ],
   "source": [
    "a = b = c = 1\n",
    "print(a, b, c)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 2 pooya\n"
     ]
    }
   ],
   "source": [
    "a, b, c = 1, 2, \"pooya\"\n",
    "print(a, b, c)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Value Error "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "too many values to unpack (expected 3)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "Input \u001b[1;32mIn [5]\u001b[0m, in \u001b[0;36m<cell line: 1>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[0m a, b, c \u001b[38;5;241m=\u001b[39m \u001b[38;5;241m1\u001b[39m, \u001b[38;5;241m2\u001b[39m, \u001b[38;5;124m\"\u001b[39m\u001b[38;5;124mpooya\u001b[39m\u001b[38;5;124m\"\u001b[39m, \u001b[38;5;124m\"\u001b[39m\u001b[38;5;124mmohammadi\u001b[39m\u001b[38;5;124m\"\u001b[39m\n",
      "\u001b[1;31mValueError\u001b[0m: too many values to unpack (expected 3)"
     ]
    }
   ],
   "source": [
    "a, b, c = 1, 2, \"pooya\", \"mohammadi\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Q: How to replace the values of two variables like below?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "a = 10\n",
    "b = 20\n",
    "print(\"a: \", a, \", b: \", b)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# A\n",
    "a, b = b, a\n",
    "print(\"a: \", a, \", b: \", b)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<a id=\"How_to_delete_a_variable\"></a>\n",
    "### Delete a variable"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "a = 10\n",
    "print('a: ', a)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'a' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "Input \u001b[1;32mIn [6]\u001b[0m, in \u001b[0;36m<cell line: 2>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[38;5;28;01mdel\u001b[39;00m a\n\u001b[1;32m----> 2\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[38;5;124m'\u001b[39m\u001b[38;5;124ma: \u001b[39m\u001b[38;5;124m'\u001b[39m, \u001b[43ma\u001b[49m)\n",
      "\u001b[1;31mNameError\u001b[0m: name 'a' is not defined"
     ]
    }
   ],
   "source": [
    "del a\n",
    "print('a: ', a)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<a id=\"How_to_use_Jupyter_notebook's_Auto-Complete\"></a>\n",
    "### Auto-Complete\n",
    "Type in the first two or three characters of a variable or a function and hit `tab`. Then Jupyter notebook's auto-complete\n",
    "1. pops up a drop down menu with several suggestions\n",
    "2. automatically completes the input if there is only one possible completion available\n",
    "3. or just does nothing if there are no completions due to misspelling, import issues etc."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "counter = 100"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'co' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "Input \u001b[1;32mIn [8]\u001b[0m, in \u001b[0;36m<cell line: 2>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[38;5;66;03m# drop down list:\u001b[39;00m\n\u001b[1;32m----> 2\u001b[0m \u001b[43mco\u001b[49m\n",
      "\u001b[1;31mNameError\u001b[0m: name 'co' is not defined"
     ]
    }
   ],
   "source": [
    "# drop down list:\n",
    "co"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'coun' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "Input \u001b[1;32mIn [9]\u001b[0m, in \u001b[0;36m<cell line: 2>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[38;5;66;03m# atomatic completion with one hit\u001b[39;00m\n\u001b[1;32m----> 2\u001b[0m \u001b[43mcoun\u001b[49m\n",
      "\u001b[1;31mNameError\u001b[0m: name 'coun' is not defined"
     ]
    }
   ],
   "source": [
    "# atomatic completion with one hit\n",
    "coun"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'coan' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "Input \u001b[1;32mIn [10]\u001b[0m, in \u001b[0;36m<cell line: 2>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[38;5;66;03m# misspelling\u001b[39;00m\n\u001b[1;32m----> 2\u001b[0m \u001b[43mcoan\u001b[49m\n",
      "\u001b[1;31mNameError\u001b[0m: name 'coan' is not defined"
     ]
    }
   ],
   "source": [
    "# misspelling\n",
    "coan"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "190\n"
     ]
    }
   ],
   "source": [
    "# How can misspelling become a pain in programming?\n",
    "counter = 200\n",
    "print(counter - 10) # your expectation is 190 but the output is 90!"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "*_:)_*"
   ]
  }
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