predicates.rst

Predicates

Predicates are functions that take something and return a boolean about truthfulness of given statement. Satella contains a bunch of functions to produce these predicates.

Satella lets you express predicates in a Pythonic way, eg:

p = x == 2

assert(p(2) and not p(1))

p = x > 2

assert(p(2) and not p(1))

This behaviour extends to operators, item procurement and attr procurement. The only exception is the length, which due to Python limitations (namely __len__ being allowed to return an int only) is called via it's method .length(), eg:

p = x.length() == 2

assert(p([1, 2]) and not p([3])

You can also piece together multiple predicates. Because of Python limitations please use & and | operators in place of and and or. Also use ^ in place of xor and ~ in place of not.

p = x > 2 & x < 6

assert(p(4) and not p(8) and not p(1))

Predicate class is documented here:

To use the predicate you are to execute the following import: