Utility Classes :: IsOnlyOneOf

Overview

The IsOnlyOneOf() is related to the IsOneOf() class, but with a major difference:

IsOneof(IsIterable(), IsCallable())

IsOnlyOneOf(IsIterable(), IsCallable())

Where IsIterable() and IsCallable() are the IsIterable() and IsCallable() utility classes, respectively.

The first signature will accept the object if it's iterable, callable or both. In the second signature, however, the object must be either callable or iterable; if it's both iterable and callable, that's a no-go.

Details

• If the object being checked by the IsOnlyOneOf instance does not match any of the provided conditions, or matches more than one of the provided conditions, a _TC_XorError will be raised; the matched_conds attribute will be either 0 or 2, and the inner attribute will be a _TC_TypeError instance.

  This exception is to be caught and converted to a TypeCheckError before it reaches the level of the user.

• IsOnlyOneOf objects will only compare equal (i.e., ==) if all the conditions in the left-hand side are found in the right-hand side, and vice versa.

  All IsOnlyOneOf instances that compare equal with == will produce the same value when run through the built-in hash() function.

• The IsOnlyOneOf class has been given some intelligence about boolean equality, meaning that it will optimise the creation of certain instances. For instance:

  IsOnlyOneOf(IsOnlyOneOf(int, float), \
  	IsOnlyOneOf(str, set))

  is equivalent to

  IsOnlyOneOf(int, float, str, set)

  In fact, the first will be coerced into the second, meaning that the two will compare and hash as equals.

• Another coercion-related intelligence is this:

  IsOnlyOneOf(int, int, float, float)

  will be simplified to

  IsOnlyOneOf(int, float)

  Again, these two will compare and hash as equals [5, 6].

• The order in which the IsOnlyOneOf instance's conditions will be checked is undefined.