005_Python_Keywords_and_Identifiers.ipynb

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    "<small><small><i>\n",
    "All the IPython Notebooks in **Python Introduction** lecture series by Dr. Milaan Parmar are available @ **[GitHub](https://github.com/milaan9/01_Python_Introduction)**\n",
    "</i></small></small>"
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   "source": [
    "# Python Keywords and Identifiers\n",
    "\n",
    "In this class, you will learn about keywords (reserved words in Python) and identifiers (names given to variables, functions, etc.)."
   ]
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    "# 1. Python Keywords\n",
    "\n",
    "Keywords are the reserved words in Python.\n",
    "\n",
    "We cannot use a keyword as a **[variable](https://github.com/milaan9/01_Python_Introduction/blob/main/009_Python_Data_Types.ipynb)** name, **[function](https://github.com/milaan9/04_Python_Functions/blob/main/001_Python_Functions.ipynb)** name or any other identifier. They are used to define the syntax and structure of the Python language.\n",
    "\n",
    "In Python, keywords are **case sensitive**.\n",
    "\n",
    "There are **36** keywords in Python 3.9. This number can vary slightly over the course of time.\n",
    "\n",
    "All the keywords except **`True`**, **`False`** and **`None`** are in lowercase and they must be written as they are. The **[list of all the keywords](https://github.com/milaan9/01_Python_Introduction/blob/main/Python_Keywords_List.ipynb)** is given below.\n",
    "\n",
    "**Keywords in Python**\n",
    "\n",
    "|     |     |     |     |\n",
    "|:----|:----|:----|:----|\n",
    "| **`False`** | **`break`** | **`for`** | **`not`** |\n",
    "| **`None`**  | **`class`** | **`from`** | **`or`** |\n",
    "| **`True`**  | **`continue`** | **`global`** | **`pass`** |\n",
    "| **`__peg_parser__`** |**`def`** | **`if`** | **`raise`** |\n",
    "| **`and`** | **`del`** | **`import`** | **`return`** |\n",
    "| **`as`** | **`elif`** | **`in`** | **`try`** |\n",
    "| **`assert`** | **`else`** | **`is`** | **`while`** |\n",
    "| **`async`** | **`except`** | **`lambda`** | **`with`** |\n",
    "| **`await`** | **`finally`** | **`nonlocal`** |  **`yield`**  |\n",
    "\n",
    "You can see this list any time by typing help **`keywords`** to the Python interpreter. \n",
    "\n",
    "Trying to create a variable with the same name as any reserved word results in an **error**:\n",
    "\n",
    "```python\n",
    ">>>for = 6\n",
    "\n",
    "File \"<ipython-input-1-50b154750974>\", line 1\n",
    "for = 6 # It will give error becasue \"for\" is keyword and we cannot use as a variable name.\n",
    "        ^\n",
    "SyntaxError: invalid syntax\n",
    "```"
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    "for = 6 # It will give error becasue \"for\" is keyword and we cannot use as a variable name."
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    "For = 6 # \"for\" is keyword but \"For\" is not keyword so we can use it as variable name\n",
    "For"
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   "source": [
    "# 2. Python Identifiers\n",
    "\n",
    "An **identifier** is a name given to entities like **class, functions, variables, etc**. It helps to differentiate one entity from another."
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    "### Rules for writing identifiers\n",
    "\n",
    "1. **Identifiers** can be a combination of letters in lowercase **(a to z)** or uppercase **(A to Z)** or digits **(0 to 9)** or an underscore **`_`**. Names like **`myClass`**, **`var_1`** and **`print_this_to_screen`**, all are valid example. \n",
    "\n",
    "2. An identifier cannot start with a digit. **`1variable`** is invalid, but **`variable1`** is perfectly fine. \n",
    "\n",
    "3. Keywords cannot be used as identifiers\n",
    "\n",
    "```python\n",
    ">>>global = 3\n",
    "\n",
    "File \"<ipython-input-2-43186c7d3555>\", line 1\n",
    "    global = 3 # because \"global\" is a keyword\n",
    "           ^\n",
    "SyntaxError: invalid syntax\n",
    "```"
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      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-3-3e859d37287a>\"\u001b[1;36m, line \u001b[1;32m1\u001b[0m\n\u001b[1;33m    global = 3 # because \"global\" is a keyword\u001b[0m\n\u001b[1;37m           ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
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    "global = 3 # because \"global\" is a keyword"
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    "4. We cannot use special symbols like **!**, **@**, **#**,<b> $, % </b>, etc. in our identifier.\n",
    "\n",
    "```python\n",
    ">>>m@ = 3\n",
    "\n",
    "File \"<ipython-input-3-4d4a0e714c73>\", line 1\n",
    "    m@ = 3\n",
    "       ^\n",
    "SyntaxError: invalid syntax\n",
    "```"
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      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-4-0f73a35e8ce2>\"\u001b[1;36m, line \u001b[1;32m1\u001b[0m\n\u001b[1;33m    m@ = 3\u001b[0m\n\u001b[1;37m       ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
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    "m@ = 3"
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    "## Things to Remember\n",
    "\n",
    "Python is a case-sensitive language. This means, **`Variable`** and **`variable`** are not the same.\n",
    "\n",
    "Always give the identifiers a name that makes sense. While **`c = 10`** is a valid name, writing **`count = 10`** would make more sense, and it would be easier to figure out what it represents when you look at your code after a long gap.\n",
    "\n",
    "Multiple words can be separated using an underscore, like **`this_is_a_long_variable`**."
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    "this_is_a_long_variable = 6+3\n",
    "this_is_a_long_variable"
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    "add_6_and_3 = 6+3\n",
    "add_6_and_3"
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