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Expressions

To perform calculations, programs use expressions. You have already used them in the first lesson!

Definition 1. An expression is a sequence of one or more operands, linked together by operators, according to programming language-specific syntactic rules.

For example, for the expression 3 + 4 * 2
3, 4 and 2 are operands, and + and * are operators.

An incorrectly written expression will lead to an interpretation error (this is called a syntax error):



During the execution of the Python program, the expressions are evaluated (i.e. a result is calculated).

Arithmetic operators can be unary or binary.

Unary operators

Unary operators (+ and -) act on a single operand that is always to the right of the operator. "+" returns the value of the operand, and "-" returns the value of the changed sign operand.

Examples: -23, +11

Binary operators

Binary operators (+, -, *, /, //, %) act on two operands. One operand is always to the left of the operator and the other to his right.

Examples: 10+5, 5-2, 7*5, etc.

We analyze some peculiarities of three operators on the next page.

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