Expressions#

An expression is a unit of code that can be solved to a single value.

This process is called evaluating the expression.

Take the following simple expression that resolves to 30.

10 * 3

It is comprised of:

# LHV    Operator   RHV
10       *          3

An operator is a symbol with special meaning that tells Python to do something. Some examples of operators include +, =, and ==.

When an expression includes an operator involved in Python, there is always a left-hand value and a right-hand value.

Let’s take a more complicated example.

2 + 3 * 6

In this case we have 2 operators: + and *. So then which is the left-hand value, and which the right-hand?

The answer is that Python evaluates this the same way we would solve a math problem. That is, it breaks it down into multiple expressions.

# Expression 1: (3 * 6)
#   LHV    Operator   RHV
2 + 3      *           6

# Expression 2: (2 + 18)
# LHV    Operator   RHV
2        +          18

Here are some examples of expressions

3                        # a stand-alone value is the simplest expression
"hello"                  # a stand-alone string value
today                    # a variable (when assigned)
yesterday = today - 1    # two expressions: #1: today - 1, #2: yesterday = 15
input()                  # functions with a return value also evaluate to a value

Anywhere that we can use a value, we can also use an expression. Python will first evaluate the expression, then use the resulting value in its place.

# using stand-alone values
print(3)
print("hello")
print(yesterday)

# first, evaluates today-1
# then sends 15 as an argument to print()
print(today-1)

# first calls the input() function and waits for the user response
# then sends the result to print()
print(input())

Self-Quiz#

  1. What is the operator in this expression?

"hello " * 3

  1. If the value of name is "Joe", what is the argument that is sent to the print() function?

print("Hello " + name)

  1. What does the following expression evaluate to?

1 == 2

Reference#

Glossary#

Expressions#

evaluate#

the process of solving an expression to its resulting value

expression#

a unit of code that can be solved to a single value

LHV#
left-hand value#

the value to the left of an operator

operator#

A symbol with special meaning that tells the computer to do something (for example =, +, or ==).

RHV#
right-hand value#

the value to the right of an operator

value#

a piece of data or information strings, integers and more.

More info#