Short-Circuit Boolean Expressions

Short-circuit boolean expressions are boolean expressions whose arguments are evaluated only when necessary.

There are two “short-circuit” boolean expressions.

Expr1 orelse Expr2

This first evaluates Expr1. If Expr1 evaluates to true, Expr2 is not evaluated. If Expr1 evaluates to false, Expr2 is evaluated.

Expr1 andalso Expr2

This first evaluates Expr1. If Expr1 evaluates to true, Expr2 is evaluated. If Expr1 evaluates to false, Expr2 is not evaluated.

Note: In the corresponding boolean expressions (A or B; A and B), both the arguments are always evaluated, even if the truth value of the expression can be determined by evaluating only the first expression.

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