4.5. Statements and Expressions

A statement is an instruction that the Python interpreter can run. So far, we have used print statements and assignment statements.

An expression is a combination of values, variables, operators, and calls to functions. Think of an expression as a formula made up of multiple parts.

# These are statements:
message = "Hello, World!"
print(24)

# This statement contains an expression:
total = 3 + 4

In line 6, before Python can assign a value to total, the expression 3 + 4 must be evaluated. This means Python figures out the result of the calculation 3 + 4, and then returns that value to the statement. The variable total does NOT store 3 + 4. Instead, it stores the result, 7.

Every expression produces a value, known as the return value. We say that an expression returns a value when it runs.

When you print an expression in Python, the interpreter evaluates the expression and displays the result.

Example

print(2 + 3)

message = "Hello, World!"
print(message)

Console Output

5
Hello, World!

Line 1 does NOT print 2 + 3. Instead, it prints the result of calculating 2 + 3, so we see 5 in the console. The expression 2 + 3 returns the value 5. Think of this as the print argument (2 + 3) getting evaluated as (5).

The statement in line 4 also has an expression. The variable message holds a string. Evaluating the variable returns that string, so print(message) becomes print("Hello, World!").