Built-in composition functions

We have seen in previous section that an implicit "and" can be easily performed. However in some cases you might need additional ways to compose functions. A few tools are provided out of the box:

not_

not_(validation_func: ValidationFunc, 
     catch_all: bool = False)

Generates the inverse of the provided validation functions: when the validator returns False or raises a ValidationFailure, this function returns True. Otherwise it raises a DidNotFail failure.

By default, exceptions of types other than ValidationFailure are not caught and therefore fail the validation (catch_all=False). To change this behaviour you can turn the catch_all parameter to True, in which case all exceptions will be caught instead of just ValidationFailures.

Note that the argument is a single callable. You may use not_all(<validation_functions_list>) as a shortcut for not_(and_(<validation_functions_list>)) to support several validation functions in the 'not'.

See help(not_)

and_

and_(*validation_func: ValidationFuncs)

An 'and' validator: it returns True if all of the provided validators return True, or raises a AtLeastOneFailed failure on the first False received or Exception caught.

Note that an implicit and_ is performed if you provide a list of validators to any of the entry points (validator/validation, @validate_arg, @validate_field ...). For validate you need to use an explicit one in custom=<f>.

See help(and_)

or_

or_(*validation_func: ValidationFuncs)

An 'or' validator: returns True if at least one of the provided validators returns True. All exceptions will be silently caught. In case of failure, a global AllValidatorsFailed failure will be raised, together with details about all validation results.

See help(or_)

xor_

xor_(*validation_func: ValidationFuncs)

A 'xor' validation function: returns True if exactly one of the provided validators returns True. All exceptions will be silently caught. In case of failure, a global XorTooManySuccess or AllValidatorsFailed will be raised, together with details about the various validation results.

See help(xor_)

not_all

not_all(*validation_func: ValidationFuncs, 
        catch_all: bool = False)

An alias for not_(and_(validators)).

See help(not_all)

skip_on_none

skip_on_none(*validation_func: ValidationFuncs)

This function is automatically used if you use none_policy=SKIP, you will probably never need to use it explicitly. If wraps the provided function (or implicit and_ between provided functions) so that None values are not validated and the code continues executing.

See help(skip_on_none)

fail_on_none

fail_on_none(*validation_func: ValidationFuncs)

This function is automatically used if you use none_policy=FAIL, you will probably never need to use it explicitly. If wraps the provided function (or implicit and_ between provided functions) so that None values are not validated instead a ValueIsNone failure is raised.

See help(fail_on_none)