Expressions, statements, input and output

An expression is a combination of values, variables and operators that always evaluates to a single value. A value or a variable on its own is also an expression (5, or total).

When an expression has several operators, Python follows an order of precedence:

• the power operator first;
• then unary minus and plus (as in -5);
• then *, /, % and //;
• then + and -;
• then the comparisons;
• then not, then and, then or.

Operators of equal precedence are worked out from left to right. Brackets override everything: what is inside them is done first.

• 5 + 4 * 3 = 5 + 12 = 17 (multiplication first).
• (5 + 4) * 3 = 9 * 3 = 27 (brackets first).
• 10 - 4 + 2 = 6 + 2 = 8 (left to right).

A statement is a unit of code that the interpreter can execute, such as x = 7 or print(x).

Input: input([prompt]) shows the prompt, waits for the user to type something, and returns it as a string, even if the user types digits. So type(input()) is always str. To use the input as a number, convert it: age = int(input('Enter age: ')).

Output: print(value, ..., sep=' ', end='\n') prints the values, separated by sep (a space by default), and finishes with end (a new line by default). For example, print('a', 'b', sep=':') prints a:b. Joining strings with + puts no space between them; separating them with a comma in print adds a space.