Validators have two important external methods:
- .to_python(value, state):
Attempts to convert the value. If there is a problem, or the
value is not valid, an Invalid exception is raised. The
argument for this exception is the (potentially HTML-formatted)
error message to give the user.
- .from_python(value, state):
Reverses to_python.
There are five important methods for subclasses to override,
however none of these have to be overridden, only the ones that
are appropriate for the validator:
- __init__():
if the
declarative.Declarative
model doesn't work for this.
- .validate_python(value, state):
This should raise an error if necessary. The value is a Python
object, either the result of to_python, or the input to
from_python.
- .validate_other(value, state):
Validates the source, before to_python, or after from_python.
It's more common to use
.validate_python()
however.
- ._to_python(value, state):
This returns the converted value, or raises an Invalid
exception if there is an error. The argument to this exception
should be the error message.
- ._from_python(value, state):
Should undo .to_python() in some reasonable way, returning
a string.
Validators should have no internal state besides the
values given at instantiation. They should be reusable and
reentrant.
All subclasses can take the arguments/instance variables:
- if_empty:
If set, then this value will be returned if the input evaluates
to false (empty list, empty string, None, etc), but not the 0 or
False objects. This only applies to .to_python().
- not_empty:
If true, then if an empty value is given raise an error.
(Both with .to_python() and also .from_python()
if .validate_python is true).
- strip:
If true and the input is a string, strip it (occurs before empty
tests).
- if_invalid:
If set, then when this validator would raise Invalid during
.to_python(), instead return this value.
- if_invalid_python:
If set, when the Python value (converted with
.from_python()) is invalid, this value will be returned.
- accept_python:
If True (the default), then .validate_python() and
.validate_other() will not be called when
.from_python() is used.
Messages
- badType:
- The input must be a string (not a %(type)s: %(value)r)
- empty:
- Please enter a value
- noneType:
- The input must be a string (not None)