Chained Comparisons

Comparison operators can be chained together to arbitrary length. For example, the following expressions are nearly equivalent:

x < y <= z
x < y and y <= z

They will both evaluate to the same Boolean value. The subtle difference between the two is that in the chained comparison x < y <= z, y is evaluated only once. The longer expression x < y and y <= z will cause y to be evaluated twice.

More generally, if op1, op2, …, opn are comparison operators, then the following have the same Boolean value:

    x1 op1 x2 op2 x3 … xn-1 opn xn

    x1 op1 x2 and x2 op2 x3 and … xn-1 opn xn

In the former case, each xi is only evaluated once. In the latter case, each will be evaluated twice except the first and last, unless short-circuit evaluation causes premature termination.