1. Introduction to Computer Science
Programming with Python

2. Loops & Iteration
Chapter 5: Loop Idioms

3. Counting in a Loop
The point of this is to keep track of the iterations
To count how many times we execute a loop, we introduce a counter variable that starts at 0 and we add one to it each time through the loop

4. Summing in a Loop
To add up a value we encounter in a loop, we introduce a sum variable that start at 0 and we add the value to the sum each time through the loop

5. Finding the Average in a Loop
An average just combines the counting and sum patterns and divides when the loop is done

6. Filtering in a Loop
if statement is used in the loop to catch/filter the values we are looking for

7. Search Using a Boolean Variable
If we just want to search and know if a value was found, we use a variable that starts at False and is set to True as soon as we find what we are looking for

8. Search Using a Boolean Variable
If we just want to search and know if a value was found, we use a variable that starts at False and is set to True as soon as we find what we are looking for
break

9. Finding Smallest Value with Negative Numbers
What do we do in this case? Will the following solution work? -1 is like a flag/indicator

10. Unknown Value - None smallest = None
None is a value that we can distinctly detect different (empty) than numbers

11. Finding the Smallest Value
We still have a variable that is the smallest so far. The first time through the loop smallest is None, so we take the first value to be the smallest

12. None/Null Values in Other Programming Languages
In Python, the null object is the singleton None
The best way to check things for Noneness is to use the identity operator is
Example, if smallest is None
The Pythonic way to assign a variable with an unknown value or nothing is to use the keywork None
In most programming languages such as Java, C#, etc, the None is null

13. The “is” and “is not” Operators
Python has an is operator that can be used in logical expressions
Implies “is the same as”
Similar to, but stronger than ==
is not also is a logical operator
They are usually used for True, False, or None
Do not use them to compare values. is is much stronger thing than comparing mathematical values