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https://github.com/daveoncode/pyvaru

Rule based data validation library for python 3.
https://github.com/daveoncode/pyvaru

data data-validation form-validation model validation validator

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Rule based data validation library for python 3.

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What is pyvaru?

---------------



Pyvaru is a simple, flexible and unobtrusive data validation library for Python 3 (3.4+),

based on the concept of validation rules.



From the software design point of view, a rule is a class implementing the strategy pattern, 

by encapsulating the validation logic in an interface method called ``apply()``.



The library already offers a series of common validation rules like:

 

- ``TypeRule`` (it checks that the target value is an instance of the expected type)

- ``FullStringRule`` (it checks the the target value is a string with content)

- ``ChoiceRule`` (it checks that the target value is contained in a list of available options)

- ``MinValueRule`` (it checks that the target value is >= x) *

- ``MaxValueRule`` (it checks that the target value is <= x) *

- ``MinLengthRule`` (it checks that the target value length is >= x) *

- ``MaxLengthRule`` (it checks that the target value length is <= x) *

- ``RangeRule`` (it checks that the target value is contained in a given ``range``)

- ``IntervalRule`` (it checks that the target value is contained in a given interval)

- ``PatternRule`` (it checks that the target value matches a given regular expression)

- ``PastDateRule`` (it checks that the target value is a date in the past)

- ``FutureDateRule`` (it checks that the target value is a date in the future)

- ``UniqueItemsRule`` (it checks that the target iterable does not contain duplicated items)

 



\* where "x" is a provided reference value



The developer is then free to create his custom rules by extending the abstract ``ValidationRule``

and implementing the logic in the ``apply()`` method. For example:



.. code-block:: python



    class ContainsHelloRule(ValidationRule):

        def apply(self) -> bool:

            return 'hello' in self.apply_to



These rules are then executed by a ``Validator``, which basically executes them in the provided

order and eventually returns a ``ValidationResult`` containing the validation response.



Installation

------------



``pip install pyvaru``



Usage

-----

    

Given an existing model to validate, like the one below

(but it could be a simple dictionary or any data structure since `pyvaru`

does not make any assumption on the data format):



.. code-block:: python



    class User:

        def __init__(self, first_name: str, last_name: str, date_of_birth: datetime, sex: str):

            self.first_name = first_name

            self.last_name = last_name

            self.date_of_birth = date_of_birth

            self.sex = sex



        

We have to define a validator, by implementing the ``get_rules()`` method and for each field we want to

validate we have to provide one or more proper rule(s).



.. code-block:: python



    from pyvaru import Validator

    from pyvaru.rules import TypeRule, FullStringRule, ChoiceRule, PastDateRule



    class UserValidator(Validator):

        def get_rules(self) -> list:

            user = self.data # type: User

            return [

                TypeRule(apply_to=user,

                         label='User',

                         valid_type=User,

                         error_message='User must be an instance of user model.',

                         stop_if_invalid=True),

                FullStringRule(lambda: user.first_name, 'First name'),

                FullStringRule(lambda: user.last_name, 'Last name'),

                ChoiceRule(lambda: user.sex, 'Sex', choices=('M', 'F')),

                PastDateRule(lambda: user.date_of_birth, 'Date of birth')

            ]



It's also possible to create groups of rules by using ``RuleGroup`` and avoid code duplication if multiple rules should

be applied to the same field. So this code:



.. code-block:: python



    def get_rules(self) -> list:

        return [

            TypeRule(lambda: self.data.countries, 'Countries', valid_type=list),

            MinLengthRule(lambda: self.data.countries, 'Countries', min_length=1),

            UniqueItemsRule(lambda: self.data.countries, 'Countries')

        ]



can be replaced by:



.. code-block:: python



    def get_rules(self) -> list:

        return [

            RuleGroup(lambda: self.data.countries,

                      'Countries',

                      rules=[(TypeRule, {'valid_type': list}),

                             (MinLengthRule, {'min_length': 1}),

                             UniqueItemsRule])

        ]



Finally we have two choices regarding how to use our custom validator:

    

1. As a context processor:



.. code-block:: python



    with UserValidator(user):

        # do whatever you want with your valid model



In this case the code inside ``with`` will be executed only if the validation succeed, otherwise a

``ValidationException`` (containing a ``validation_result`` property with the appropriate report) is raised.

        

2. By invoking the ``validate()`` method (which returns a ``ValidationResult``)



.. code-block:: python



    validation = UserValidator(user).validate()

    if validation.is_successful():

        # do whatever you want with your valid model

    else:

        # you can take a proper action and access validation.errors

        # in order to provide a useful message to the application user,

        # write logs or whatever



Assuming we have a instance of an User configured as the one below:



.. code-block:: python



    user = User(first_name=' ',

                last_name=None,

                date_of_birth=datetime(2020, 1, 1),

                sex='unknown')



By running a validation with the previous defined rules we will obtain a ``ValidationResult`` with the following errors:



.. code-block:: python



    {

        'First name': ['String is empty.'],

        'Last name': ['Not a string.'],

        'Sex': ['Value not found in available choices.'],

        'Date of birth': ['Not a past date.']

    }



Full API Documentation

----------------------



Go to: http://pyvaru.readthedocs.io/en/latest/contents.html



Credits

-------



Pyvaru is developed and maintained by Davide Zanotti.



Blog: http://www.daveoncode.com



Twitter: https://twitter.com/daveoncode