We’ll start off a little slow and talk about expressions in python. From your math classes, you probably know that an expression is anything that can be evaluated, like 24+3, 5/2, 6.72, etc..
In Python, expressions are pretty much the same – anything that can be evaluated.
Primitive values in Python include numbers and booleans, which evaluate to themselves. Generally, anything that evaluates to itself in one step is a primitive expression.
>>> 27
27
>>> False
False
>>> 4.27
4.27
Each of these is a primitive expression, as no computation is required to evaluate them.
This is just math! Python comes with the four basic arithmetic operators – +, -, *, / – as well as a few more than you’ll find useful in your CS experience.
**: this is the exponentiation operator; the equivalent of $2^2$ in Python is 2**2.//: this is the floor division operator; it will round down the result of division and return an integer.%: this is the modulo operator; it will evaluate to the positive remainder from division.The regular division operator returns a floating-point number, even if the numbers divide evenly. For example, 3/3 will return 1., not 1. See the difference?
On the other hand, the floor division and modulo operators will return integers.
Python also respects PEMDAS.
>>> 3 + 2
5
>>> 3 % 2
1
>>> 3 / 2
1.5
>>> 3 // 2 # floor division rounds down!
1
>>> (3 + 2) / 5
1.0
>>> 6 % 4 # the positive remainder of 6/4
2
In Python, as with any other programming language, you can assign values to variable names. This allows to reuse and update values as your code executes, giving you more flexibility and functionality.
Assigning a variable is as simple as setting it equal to the result of an expression:
>>> c = 5 + 2
>>> c
7
An important note made in Lab 0 that I’d like to reiterate here is that names are bound to values, not expressions. The statement above will first evaluate 5 + 2 = 7 and then set c = 7.