If Statements
=============

If Statement videos
-------------------
- `Python Tutorial for Beginners 6: Conditionals and Booleans - If, Else, and Elif Statements <https://www.youtube.com/watch?v=DZwmZ8Usvnk>`_

    - ``if/elif/else``
    - ``and``, ``or``, ``not``
    - ``is`` and ``id()``
    - "Truthy" and "Falsey" Values

Comparison operators
--------------------
.. code-block:: python

    >   # greater than
    <   # less than
    >=  # greater than or equal to
    <=  # less than or equal to
    ==  # equal to
    !=  # not equal to
    is  # used to check equality for True, False, and None
    in  # determines if something is in a collection


if, else
--------
.. code-block:: python

    age = int(input("Please enter your age: "))

    if age >= 18:
        print("You can vote")
    else:
        print("You can not vote.")


if, elif, else
--------------
.. code-block:: python
    
    mark = int(input("Please enter your mark: "))

    if mark >= 80:
        print("You have an A")
    elif mark >= 70:
        print("You have a B")
    else:
        print("You have a C or lower.")


Multiple elif
-------------
.. code-block:: python

    mark = int(input("Please enter your mark: "))

    if mark >= 80:
        print("You have an A")
    elif mark >= 70:
        print("You have a B")
    elif mark >= 60:
        print("You have a C")
    elif mark >= 50:
        print("You have a D")
    else:
        print("You FAIL!!!!")


Boolean values in variables
---------------------------
.. code-block:: python

    age = 10
    old_enough = age > 5

    if old_enough is True:
        print("You can ride on the rollercoaster!")


Boolean operators
-----------------
We need to be able to reproduce these truth tables.

AND
***
*Both* inputs need to be ``True``. Think: **"Both And"**.

=====  =====  =======
A      B      A and B
=====  =====  =======
True   True   True
True   False  False
False  True   False
False  False  False
=====  =====  =======

OR
**
*Either* can be ``True``. Think: **"Either Or""**.

=====  =====  ======
A      B      A or B
=====  =====  ======
True   True   True
True   False  True
False  True   True
False  False  False
=====  =====  ======

NOT
***
Inverts the Boolean value.

=====  =====
A      not A
=====  =====
True   False
False  True
=====  =====

.. raw:: html

    <iframe width="560" height="315" src="https://www.youtube.com/embed/inxWNWy1nMA" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>


Boolean operators in if statements
----------------------------------
.. code-block:: python

    a = 5
    b = 7

    if a >= 5 and b > 10:  # False
        print("hello")

    if a == 5 or b > 100:  # True
        print("goodbye")

    if not (a >= 5 and b > 10):  # True
        print("hello")