1. Bools and simple if statements
Decisions in Python
Bools and simple if statements

2. Computer logic is Boolean
George Boole, 19th cent. English mathematician, logician
Had the idea to do logic with two values True and False
Computer logic is based on exactly that
Making decisions in a computer is based on two-valued logic, results are either True or False
Python has two predefined constants (literals): True and False (note, no quotes)
Several operators will give Boolean results

3. Relational Operators
Familiar from algebra: >, <, >=, <=, ==, !=
Relational operators give the “relationship” between two things
They can compare many different types, but be careful to compare things of the same type, ints and floats are ok, ints and strings are not
They compare the two operands and give True or False as a result
Comparing numbers is fairly routine
Be careful about comparing floats to floats for exact equality
The way floats are stored may cause some numbers that you think should be equal NOT to be equal
Precedence of all of these operators is lower than the arithmetic operators and all six of them have the same precedence

4. Where to use them?
You can use them to generate Bools and store the results
X_larger = x > y # stores True or False in X_larger
the_same = x == y # stores True or False in the_same
Most often use the results in an if statement

5. if statement syntax statement starts with the word if
immediately followed by some expression which has a Bool value
then a colon
next will be at least one statement indented more than the if statement, usually several statements

6. if statement semantics
When an if statement is encountered in execution
First the expression that gives the Boolean value will be evaluated
If the result is True, the statements which are indented after the if will all be executed
If the result of the expression is False, the statements which are indented will be skipped
In either case execution continues at the next statement after the if statement