Variables, Primitives, and Operators

Variables

In python, variables are assigned with the assignment operator: =.

Python naming convention: use snake_case for variables (except for specific exceptions, discussed later).

Variables

Variables store their value to be used later. We've already seen this use with the print function!

Overwriting

Variables in python can be overwritten. Python won't complain.

This can be nice. It can also be dangerous if you don't realize you're overwriting a variable!

To avoid this, we try to minimize the number of variables we have at any time. We will see strategies for this later.

Primitive Data Types

Variables can hold all different types of data. Here are some of the main primitive data types in Python:

int is an integer (number).
float is a decimal number.
str is a string (characters/words).
bool is a binary value: true or false.
None is a special type for no value!

Combining values

Often we want to combine two values into a single value.

We can add two numbers (ints or floats) with the + operator.

We can also concatenate two strings with the + operator.

Note: in each case, the operator returns the same data type as the two values it was given (more or less).

Boolean logic

We can also combine two booleans into a single boolean!

and returns true if both values are True (or truthy).

or returns true if either value is True (or truthy).

Math

Numbers have many more arithmetic operators.

What do all the following do?

Once again, each of these operators takes two numbers and returns a single number.

Math

We also might want to compare numbers to each other. We can do that with these comparrison operators.

These operators take two numbers and return what data type?

Comparing values

The equality operators (== and !=) are also used for strings!

The equality operators return a boolean too. This is very useful for checking if a variable holds a certain value.

Comparing values

The equality operator (==) is also used for strings!

The equality operator returns a boolean. This is very useful for checking if a variable holds a certain value.

None

None is a very special value. It represents a lack of value!

It's very important to keep track of missing data. It's also very import to check if a variable is None or not.

We can check if a variable is None with the is operator.

Not

The not operator returns the opposite of what it is given.

is and not are also used for bool types (True and False).