Key takeaways

1. An expression is a combination of values (or variables, operators, calls to functions - you will learn about them soon) which evaluates to a value, e.g., 1 + 2.

2. Operators are special symbols or keywords which are able to operate on the values and perform (mathematical) operations, e.g., the * operator multiplies two values: x * y.

3. Arithmetic operators in Python: + (addition), - (subtraction), * (multiplication), / (classic division - returns a float if one of the values is of float type), % (modulus - divides left operand by right operand and returns the remainder of the operation, e.g., 5 % 2 = 1), ** (exponentiation - left operand raised to the power of right operand, e.g., 2 ** 3 = 2 * 2 * 2 = 8), // (floor/integer division - returns a number resulting from division, but rounded down to the nearest whole number, e.g., 3 // 2.0 = 1.0)

4. A unary operator is an operator with only one operand, e.g., -1, or +3.

5. A binary operator is an operator with two operands, e.g., 4 + 5, or 12 % 5.

6. Some operators act before others - the hierarchy of priorities:

• unary + and - have the highest priority
• then: **, then: *, /, and %, and then the lowest priority: binary + and -.

7. Subexpressions in parentheses are always calculated first, e.g., 15 - 1 * (5 * (1 + 2)) = 0.