Expressions and Instructions

Objectives

understand the difference between expressions and instructions in Python, as well as their role in a program
importance of these two concepts for writing readable and efficient Python code

Definitions and differences

An expression is a combination of values, variables, operators and functions that is evaluated to produce a value.
An expression always returns a value

Simple examples:

2 + 3   # evaluates to 5
x * 10  # evaluates to the value of x multiplied by 10
"Hello" + " World" # evaluates to "Hello World"

More complex examples:

(x + y) / 2
len("Python") > 5

Examples of instructions:

x = 5       # Assignment instruction
print(x)    # Display instruction
if x > 0:   # Conditional instruction
    print("Positive")

Types of expressions:
- Arithmetic expressions: 2 + 3, x - 1
- Boolean expressions: x > 5, y == 0
- String expressions: "Hello" + "World"
Expression evaluation:
- Explain how Python evaluates expressions from left to right, respecting operator precedence rules.
Using expressions in instructions:
- An expression can be used inside an instruction:

y = (x + 5) * 2  # Expression (x + 5) * 2 used in an assignment instruction

Types of instructions:
- Assignment instruction: x = 10
- Control flow instruction: if, for, while
- Function instruction: def my_function():
- Import instruction: import math
Compound and simple instructions:
- Simple instructions: A single line of code, for example x = 10.
- Compound instructions: Consist of multiple lines of code and include a code block (for example, loops and conditions).
Using expressions in instructions:
- Expressions are commonly used in conditional instructions or loops:

if (x + 5) > 10:  # The expression (x + 5) > 10 is used to test the condition
    print("The condition is true.")