django.core-validators
这里validators模块主要的特点是， 用类继承来模仿函数的调用。具体实现：定义class的__call__方法。
并且往往子类通过重新定义父类的属性，来达到继承的效果。
@deconstructible
class BaseValidator(object):
compare = lambda self, a, b: a is not b
clean = lambda self, x: x
message = _('Ensure this value is %(limit_value)s (it is %(show_value)s).')
code = 'limit_value'
def __init__(self, limit_value, message=None):
self.limit_value = limit_value
if message:
self.message = message
def __call__(self, value):
cleaned = self.clean(value)
params = {'limit_value': self.limit_value, 'show_value': cleaned, 'value': value}
if self.compare(cleaned, self.limit_value):
raise ValidationError(self.message, code=self.code, params=params)
def __eq__(self, other):
return (
isinstance(other, self.__class__) and
(self.limit_value == other.limit_value)
and (self.message == other.message)
and (self.code == other.code)
)
BaseValidator是一个基类，MaxValueValidator，MinValueValidator， MinLengthValidator， MaxLengthValidator都是它的子类。其中clean属性负责生成比较值， compare属性负责比较规则。limit_value是有__init__方法初始化的，用于compare的参数。
@deconstructible
class MaxValueValidator(BaseValidator):
compare = lambda self, a, b: a > b
message = _('Ensure this value is less than or equal to %(limit_value)s.')
code = 'max_value'
@deconstructible
class MinValueValidator(BaseValidator):
compare = lambda self, a, b: a < b
message = _('Ensure this value is greater than or equal to %(limit_value)s.')
code = 'min_value'
@deconstructible
class MinLengthValidator(BaseValidator):
compare = lambda self, a, b: a < b
clean = lambda self, x: len(x)
message = ungettext_lazy(
'Ensure this value has at least %(limit_value)d character (it has %(show_value)d).',
'Ensure this value has at least %(limit_value)d characters (it has %(show_value)d).',
'limit_value')
code = 'min_length'
@deconstructible
class MaxLengthValidator(BaseValidator):
compare = lambda self, a, b: a > b
clean = lambda self, x: len(x)
message = ungettext_lazy(
'Ensure this value has at most %(limit_value)d character (it has %(show_value)d).',
'Ensure this value has at most %(limit_value)d characters (it has %(show_value)d).',
'limit_value')
code = 'max_length'
deconstructible是一个类装饰器，主要功能是增加了deconstruct方法和_constructor_args属性。deconstruct方法主要返回模块名和类名，_constructor_args参数。
def deconstructible(*args, **kwargs):
"""
Class decorator that allow the decorated class to be serialized
by the migrations subsystem.
Accepts an optional kwarg `path` to specify the import path.
"""
path = kwargs.pop('path', None)
def decorator(klass):
def __new__(cls, *args, **kwargs):
# We capture the arguments to make returning them trivial
obj = super(klass, cls).__new__(cls)
obj._constructor_args = (args, kwargs)
return obj
def deconstruct(obj):
"""
Returns a 3-tuple of class import path, positional arguments,
and keyword arguments.
"""
# Python 2/fallback version
if path:
module_name, _, name = path.rpartition('.')
else:
module_name = obj.__module__
name = obj.__class__.__name__
# Make sure it's actually there and not an inner class
module = import_module(module_name)
if not hasattr(module, name):
raise ValueError(
"Could not find object %s in %s.\n"
"Please note that you cannot serialize things like inner "
"classes. Please move the object into the main module "
"body to use migrations.\n"
"For more information, see "
"https://docs.djangoproject.com/en/dev/topics/migrations/#serializing-values"
% (name, module_name))
return (
path or '%s.%s' % (obj.__class__.__module__, name),
obj._constructor_args[0],
obj._constructor_args[1],
)
klass.__new__ = staticmethod(__new__)
klass.deconstruct = deconstruct
return klass
if not args:
return decorator
return decorator(*args, **kwargs)