We start with a simple credential validation example. Before we proceed let setup virtualenv environment:

$ virtualenv env
$ env/bin/easy_install wheezy.validation

Credential Validation

Domain Model

Our domain model requires that user enter valid credentials during sigin, so Credential model might look like this:

class Credential(object):

    def __init__(self):
        self.username = ''
        self.password = ''


We know that username is a string between 2 and 20 in length, while password must have at least 8 characters and we would like limit it by 12. Both username and password are required and we need a separate message for this case. Here is credential_validator that serves our purpose:

from wheezy.validation import Validator
from wheezy.validation.rules import length
from wheezy.validation.rules import required

credential_validator = Validator({
    'username': [required, length(min=2, max=20)],
    'password': [required, length(min=8, max=12)]

Since validator in no way dependent on object it is going to validate, it can be reused in any combination, the only requirement that attributes defined in validator must exist in object you are going to validate.


Now we can proceed with validation:

credential = Credential()
errors = {}
succeed = credential_validator.validate(credential, results=errors)

errors dictionary contains all errors reported during validation. Key corresponds to attribute being checked, while value is a list of errors.

Credential Update

Web form submit is a dictionary where key is the name of the input element being submitted and value is a list. That list can have just one item for elements like input or several values that depict user choice.

Let assume form submitted values look this way:

values = {'username': [''], 'password': ['']}

Our attempt to update Credential model with values:

from wheezy.validation.model import try_update_model

credential = Credential()
errors = {}
succeed = try_update_model(credential, values, errors)

errors dictionary contains all errors reported during model update. Key corresponds to attribute being updated, while value is a list of errors.

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