intro-to-python/01_elements/05_summary.ipynb

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    "# Chapter 1: Elements of a Program (TL;DR)"
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    "We end each chapter with a summary of the main points (i.e., **TL;DR** = \"too long; didn't read\"). The essence in this first chapter is that just as a sentence in a real language like English may be decomposed into its parts (e.g., subject, predicate, and objects), the same may be done with programming languages.\n",
    "\n",
    "- program\n",
    "  - **sequence** of **instructions** that specify how to perform a computation (= a \"recipe\")\n",
    "  - a \"black box\" that processes **inputs** and transforms them into meaningful **outputs** in a *deterministic* way\n",
    "  - conceptually similar to a mathematical function $f$ that maps some input $x$ to an output $y = f(x)$\n",
    "\n",
    "\n",
    "- input (examples)\n",
    "  - data from a CSV file\n",
    "  - text entered on a command line\n",
    "  - data obtained from a database\n",
    "  - etc.\n",
    "\n",
    "\n",
    "- output (examples)\n",
    "  - result of a computation (e.g., statistical summary of a sample dataset)\n",
    "  - a \"side effect\" (e.g., a transformation of raw input data into cleaned data)\n",
    "  - a physical \"behavior\" (e.g., a robot moving or a document printed)\n",
    "  - etc.\n",
    "\n",
    "\n",
    "- objects\n",
    "  - distinct and well-contained areas/parts of the memory that hold the actual data\n",
    "  - the concept by which Python manages the memory for us\n",
    "  - can be classified into objects of the same **type** (i.e., same abstract \"structure\" but different concrete data)\n",
    "  - built-in objects (incl. **literals**) vs. user-defined objects (cf., [Chapter 11 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/11_classes/00_content.ipynb))\n",
    "  - e.g., `1`, `1.0`, and `\"one\"` are three different objects of distinct types that are also literals (i.e., by the way we type them into the command line Python knows what the value and type are)\n",
    "\n",
    "\n",
    "- variables\n",
    "  - storage of intermediate **state**\n",
    "  - are **names** referencing **objects** in **memory**\n",
    "  - e.g., `x = 1` creates the variable `x` that references the object `1`\n",
    "\n",
    "\n",
    "- operators\n",
    "  - special built-in symbols that perform operations with objects in memory\n",
    "  - usually, operate with one or two objects\n",
    "  - e.g., addition `+`, subtraction `-`, multiplication `*`, and division `/` all take two objects, whereas the negation `-` only takes one\n",
    "\n",
    "\n",
    "- expressions\n",
    "  - **combinations** of **variables** (incl. **literals**) and **operators**\n",
    "  - do *not* change the involved objects/state of the program\n",
    "  - evaluate to a **value** (i.e., the \"result\" of the expression, usually a new object)\n",
    "  - e.g., `x + 2` evaluates to the (new) object `3` and `1 - 1.0` to `0.0`\n",
    "\n",
    "\n",
    "- statements\n",
    "  - instructions that **\"do\" something** and **have side effects** in memory\n",
    "  - (re-)assign names to (different) objects, *change* an existing object *in place*, or, more conceptually, *change* the state of the program\n",
    "  - usually, work with expressions\n",
    "  - e.g., the assignment statement `=` makes a name reference an object\n",
    "\n",
    "\n",
    "- comments\n",
    "  - **prose** supporting a **human's understanding** of the program\n",
    "  - ignored by Python\n",
    "\n",
    "\n",
    "- functions (cf., [Chapter 2 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/02_functions/00_content.ipynb))\n",
    "  - named sequences of instructions\n",
    "  - the smaller parts in a larger program\n",
    "  - make a program more modular and thus easier to understand\n",
    "  - include [built-in functions <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html) like [print() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#print), [sum() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#sum), or [len() <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_py.png\">](https://docs.python.org/3/library/functions.html#len)\n",
    "\n",
    "\n",
    "- flow control (cf., [Chapter 3 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/03_conditionals/00_content.ipynb) and [Chapter 4 <img height=\"12\" style=\"display: inline-block\" src=\"../static/link/to_nb.png\">](https://nbviewer.jupyter.org/github/webartifex/intro-to-python/blob/develop/04_iteration/00_content.ipynb))\n",
    "  - expression of **business logic** or an **algorithm**\n",
    "  - conditional execution of parts of a program (e.g., `if` statements)\n",
    "  - repetitive execution of parts of a program (e.g., `for`-loops)"
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