Control flow

Comparison operators

Python provides conventional relational operators to compare values

operator	description
<	less than
>	greater than
==	is equal to
!=	is not equal to
<=	less than or equal to
>=	greater than or equal to

Here are some examples

1 < 2
2 > 1
1 == 1
1 != 2
2 <= 3
3 >= 2

These will return a bool result.

Boolean operators

Also referred to as logical operators, boolean operators are used to create conjunctions

operator	desription	logic symbol
and	logical and	p ∧ q
or	logical or	p ∨ q
not	logical not	¬p

Here are some examples

2 > 1 and 2 < 3
True or False
True and not False

These will return a bool result.

Truthiness of values

Python will interpret empty values as False and non-empty values as True. For example, it's common to execute a block of code if a list is empty. One way to do this would be

a = []

if len(a) == 0:
    print('the list is empty')

However, since Python will interpret an empty list as False you can do the following

if not a:
    print('the list is empty')

Other values that evaluate to False include an empty string '', an empty dictionary {}, the integer value 0, the float value 0.0, an empty tuple (), an empty set set(), and None.

Exercises

Exercise 1

Play around with conditional operators. Specifically, you should try comparing two strings with the less-than or greater-than operators.