Add initial version of chapter 04's summary

04_iteration/05_summary.ipynb

@@ -0,0 +1,79 @@
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+    "# Chapter 4: Recursion & Looping (TL;DR)"
+   ]
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+    "**Iteration** is about **running blocks of code repeatedly**.\n",
+    "\n",
+    "There are two redundant approaches to achieving that.\n",
+    "\n",
+    "First, we combine functions that call themselves with conditional statements. This concept is known as **recursion** and suffices to control the flow of execution in *every* way we desire. For a beginner, this approach of **backward** reasoning might not be intuitive, but it turns out to be a handy tool to have in one's toolbox.\n",
+    "\n",
+    "Second, the `while` and `for` statements are alternative and potentially more intuitive ways to express iteration as they correspond to a **forward** reasoning. The `for` statement is **syntactic sugar** that allows rewriting common occurrences of the `while` statement concisely. Python provides the `break` and `continue` statements as well as an optional `else`-clause that make working with the `for` and `while` statements even more convenient.\n",
+    "\n",
+    "**Iterables** are any **concrete data types** that support being looped over, for example, with the `for` statement. The idea behind iterables is an **abstract concept** that may or may not be implemented by any given concrete data type. For example, both `list` and `range` objects can be looped over. The `list` type is also a **container** as any given `list` objects \"contains\" references to other objects in memory. On the contrary, the `range` type does not reference any other object but instead creates *new* `int` objects \"on the fly\" (i.e., when being looped over)."
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README.md

@@ -110,6 +110,7 @@ Alternatively, the content can be viewed in a web browser
     - [exercises <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/04_exercises.ipynb)
       [<img height="12" style="display: inline-block" src="static/link/to_mb.png">](https://mybinder.org/v2/gh/webartifex/intro-to-python/develop?urlpath=lab/tree/04_iteration/04_exercises.ipynb)
       (Throwing Dice)
+    - [summary <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/05_summary.ipynb)
 
 
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