adds import

learning_python3.md

@@ -716,9 +716,59 @@ pretty_print("Alice", "-")
 
 # Using the standard library
 
-TODO import random exercise (digital dice)
-TODO import datetime exercise (will it be Sunday)
-TODO simple ROT13 cryptography with multiple libs
+There is no need to reinvent the wheel each time you build a bike.
+The same goes for programming.
+Most, if not all, programming languages come with a **standard library** which is a collection of additional objects and functions to facilitate common problems.
+We'll look at some essential ones together but I urge you to [read](https://docs.python.org/3/library/index.html) up a bit when you have some free time.
+Over the course of you programming journey you'll discover that efficient programming is often finding the right libraries and chaining them together to suit your use case.
+
+Imagine we want to include a dice in our text based adventure game.
+How on earth do we program that?
+We need some for of *randomness* in our code.
+A [quick google](https://stackoverflow.com/questions/28705965/python-random-function-without-using-random-module) demonstrates this is quite difficult without the use of libraries.
+As randomness is both [extensively](https://www.random.org/randomness/) used in programming **and** it's quite [difficult](https://medium.com/swlh/random-functions-a4f36b1dfd8f) to do properly, you'll find a `random` library in most languages.
+
+The new **keyword** you'll learn here is `import`.
+It allows you to add extra functionality to your program.
+Once *imported* we can **call** functions that exist from the library in question.
+So, our dice becomes as follows.
+
+```python3
+import random
+
+throw = random.randint(1, 6)
+
+print(throw)
+```
+
+⛑ **Autocomplete is your friend. You can use it to browse around a library and discover interesting functions or classes you can make use of.**
+
+A second widely used library is `datetime`.
+It facilitates handling dates, hours, calendars, time differences, etc.
+A simple program we can write to illustrate it's purpose is a *will-it-be-Sunday* program.
+You give date and the program tells you if it's a Sunday or not.
+
+```python3
+import datetime
+
+sunday = 6
+
+date = input("which date should I look up? (example: 2022 3 23) ")
+year, month, day = date.split()
+
+date = datetime.date(int(year), int(month), int(day))
+
+if date.weekday() == sunday:
+    print("yes! you can sleep in...")
+else:
+    print("better set your alarm")
+```
+
+The program above incorporates a lot of different concepts.
+Read it very slowly and think about what each step is doing.
+Also think about how you can *break* this program!
+
+⛑ **Why on earth is Sunday six? Read the [doc](https://docs.python.org/3/library/datetime.html#datetime.date.weekday)!**
 
 # Coding challenge - Memento Mori calculator
 
@@ -751,6 +801,7 @@ TODO guess the number exercise
 # For loop
 
 TODO say hello to my friends exercise
+TODO simple ROT13 cryptography with multiple libs
 
 # Coding challenge - Cheerleader chant