magni.utils.validation package

Subpackage providing validation capability.

The intention is to validate all public functions of the package such that erroneous arguments in calls are reported in an informative fashion rather than causing arbitrary exceptions or unexpected results. To avoid performance impairments, the validation can be disabled globally.

Routine listings

Module providing abstract superclasses for validation.
Decorate a validation function (see Notes).
Disable validation globally (see Notes).
Enable validating inputs only once (see Notes).
validate_generic(name, type, value_in=None, len_=None, keys_in=None,
has_keys=None, superclass=None, ignore_none=False, var=None) Validate non-numeric objects.
validate_levels(name, levels)
Validate containers and mappings as well as contained objects.
validate_numeric(name, type, range_=’[-inf;inf]’, shape=(), precision=None,
ignore_none=False, var=None) Validate numeric objects.
Decorate a function to allow for a one-time input validation (see Notes).


To be able to disable validation (and to ensure consistency), every public function or method should define a nested validation function with the name ‘validate_input’ which takes no arguments. This function should be decorated by decorate_validation, be placed in the beginning of the parent function or method, and be called as the first thing after its definition.

Functions in magni may be decorated by validate_once. If the validate once functionality is enabled, these functions only validate their input arguments on the first call to the function.


If, for example, the following function is defined:

>>> def greet(person, greeting):
...     print('{}, {} {}.'.format(greeting, person['title'], person['name']))

This function expects its argument, ‘person’ to be a dictionary with keys ‘title’ and ‘name’ and its argument, ‘greeting’ to be a string. If, for example, a list is passed as the first argument, a TypeError is raised with the description ‘list indices must be integers, not str’. While obviously correct, this message is not excessively informative to the user of the function. Instead, this module can be used to redefine the function as follows:

>>> from magni.utils.validation import decorate_validation, validate_generic
>>> def greet(person, greeting):
...     @decorate_validation
...     def validate_input():
...         validate_generic('person', 'mapping', has_keys=('title', 'name'))
...         validate_generic('greeting', 'string')
...     validate_input()
...     print('{}, {} {}.'.format(greeting, person['title'], person['name']))

If, again, a list is passed as the first argument, a TypeError with the description “The value(s) of >>type(person)<<, <type ‘list’>, must be in (‘mapping’,).” is raised. Now, the user of the function can easily identify the mistake and correct the call to read:

>>> greet({'title': 'Mr.', 'name': 'Anderson'}, 'You look surprised to see me')
You look surprised to see me, Mr. Anderson.