repoze.formapi 0.5.3

Minimalistic form library.

Overview
========

The ``repoze.formapi`` provides a form library which integrates with
HTML forms instead of abstracting them away.

It provides a small framework to take you through the entire process
of rendering a form, provide default values, validate and execute form
actions.

Form fields are defined using Python base types which map out nested
data structures with end points that are either integers, strings,
floats or tuples of these. It's up to the application to bridge these
with more complex objects.


Using `repoze.formapi`
======================

This library helps you marshall and validate form input as well as
execute form actions.

In the most simple usage, we'll marshall the input data:

>>> fields = {
... 'items': [int]
... }

The ``marshall`` function takes two arguments: the parameter list and
the fields definition:

>>> data, errors = formapi.marshalling.marshall(
... [('items', 1), ('items', 2), ('other', '...')], fields
... )

There were no errors:

>>> bool(errors)
False

We expect an integer list as the value for ``'item'``:

>>> data['items']
[1, 2]

To create a form you subclass the ``repoze.formapi.Form`` class and
define the form field definitions in the ``fields`` attribute.

>>> class TapeForm(formapi.Form):
... """A form to edit a casette tape object."""
...
... fields = {
... 'artist': unicode,
... 'title': unicode,
... 'asin': str,
... 'year': int,
... 'playtime': float}

There are many forms for which default values don't apply (e.g. search
forms or `add forms`); such forms can be instantiated with no
arguments:

>>> form = TapeForm()

The form data is available from the ``data`` attribute. Since we
didn't pass in a request, there's no data available.

>>> form.data['artist'] is None
True

In a web application, usually we'll anticipate data coming in through
the request object. Values are then reflected in the form data. We can
also validate the request against the form fields.

We pass the request to the form as keyword argument.

>>> request = Request(
... params=(('title', u'Motorcity Detroit USA Live'),))
>>> form = TapeForm(request=request)

This will set the title of the record on the form data object. Since
it's a valid unicode string, we expect no validation errors.

>>> form.validate()
True
>>> 'title' in form.errors
False
>>> form.data['title']
u'Motorcity Detroit USA Live'

Alternatively we can pass in the ``params`` attribute directly.

>>> form = TapeForm(params=request.params)
>>> form.data['title']
u'Motorcity Detroit USA Live'

We'll often want to initialize the form with default values. To this
effect we pass in a dictionary object.

>>> data = {
... 'artist': u'Bachman-Turner Overdrive',
... 'title': u'Four Wheel Drive',
... 'asin': 'B000001FL8',
... 'year': 1975,
... 'playtime': 33.53}
>>> form = TapeForm(data)

The values are available in the form data object.

>>> form.data['title']
u'Four Wheel Drive'

However, if we pass in the request from the former example, we'll see
that values from the request are used before the passed dictionary
object is queried.

>>> form = TapeForm(data, request=request)
>>> form.data['title']
u'Motorcity Detroit USA Live'

The provided ``data`` dictionary is unchanged at this point:

>>> data['title']
u'Four Wheel Drive'

We need to invoke the ``save`` method to commit the changes to the
provided dictionary.

>>> form.data.save()
>>> data['title']
u'Motorcity Detroit USA Live'


Additional validation
---------------------

It is possible to create validation methods for more complex
needs. These extra validators can be hooked up using the `validator`
decorator.

>>> class CDForm(formapi.Form):
... fields = {
... 'artist': unicode,
... 'title': unicode,
... 'asin': str,
... 'year': int,
... 'genre': str,
... 'playtime': float}
...
... @formapi.validator
... def check_genre(self):
... if self.data['genre'] != 'rock':
... yield 'Genre is invalid'

A validator can look at all the data that is available. This makes it
easy to create validators that need to check multiple fields.

>>> form = CDForm()
>>> form.validate()
False

The errors attribute contains our error message.

>>> form.errors[0]
'Genre is invalid'

Errors can also be assigned to a specific field. To do this a
validator can register itself for a specific field.

>>> class CDForm(formapi.Form):
...
... fields = {
... 'artist': unicode,
... 'title': unicode,
... 'asin': str,
... 'year': int,
... 'genre': str,
... 'playtime': float}
...
... @formapi.validator('genre')
... def check_genre(self):
... if self.data['genre'] != 'rock':
... yield 'Genre is invalid'

When this form is validated it will have the error available for the
specific field.

>>> form = CDForm()
>>> form.validate()
False
>>> 'genre' in form.errors
True
>>> form.errors['genre'][0]
'Genre is invalid'

Form context
------------

We can set the context of a form to some object.

>>> class Tape:
... title = u'Motorcity Detroit USA Live'
... asin = 'B000001FL8'
... year = 1975

>>> tape = Tape()

The form data will draw defaults from the context.

>>> form = TapeForm(context=tape)
>>> form.data['title']
u'Motorcity Detroit USA Live'

Request parameters take priority over the context. In the following
example, we submit the form with trivial input.

>>> request = Request(params=(('asin', u''), ('year', u'')))
>>> form = TapeForm(context=tape, request=request)

This form input is valid; although ``year`` is an integer field, the
trivial input is valid and will be assigned a value of ``None``.

>> form.validate()
True

The ``asin`` input is coerced to a string (from unicode).

>>> form.data['asin']
''

The ``year`` input is trivial. It's not a required field, so the value
is ``None`` (treated as a non-input).

>>> form.data['year'] is None
True

Required fields
---------------

We use the ``required`` method to mark fields required.

>>> from repoze.formapi import required

Let's continue the example from above. If we make the fields required,
the input no longer validates.

>>> TapeForm.fields['year'] = required(int, u"Required field" )
>>> TapeForm.fields['asin'] = required(str)

The form input is no longer valid.

>>> form = TapeForm(context=tape, request=request)
>>> form.validate()
False

>>> form.data['year'] is None
True

The error message is available as well:
>>> form.errors['year'][0]
'Required field'

>>> request = Request(params=(('asin', u'B000001FL8'), ('year', u'1978')))
>>> form = TapeForm(context=tape, request=request)

This is a valid input. We can expect both required fields to be
converted and correctly typed.

>>> form.validate()
True

>>> form.data['asin']
'B000001FL8'

>>> form.data['year']
1978

Form submission
---------------

If a form prefix has not been set, the request is applied by
default. However, most applications will want to set a form prefix and
require explicit form submission.

A form submits a "default action" if the prefix is submitted as a
parameter.

>>> request = Request(params=(
... ('tape_form', ''),
... ('title', u'Motorcity Detroit USA Live')))
>>> form = TapeForm(request=request, prefix='tape_form')
>>> form.data['title']
u'Motorcity Detroit USA Live'

As expected, if we submit a form with a different prefix, the request
is not applied.

>>> form = TapeForm(request=request, prefix='other_form')
>>> form.data['title'] is None
True

We can also define form actions on the form class itself.

>>> class TapeAddForm(TapeForm):
... """An add-form for a casette tape."""
...
... @formapi.action
... def handle_add(self, data):
... print "add"
...
... @formapi.action("add_and_edit")
... def handle_add_and_edit(self, data):
... print "add_and_edit"

The first action is a "default action"; if we submit the request we
set up before, this action will be read to be submitted.

>>> form = TapeAddForm(request=request, prefix='tape_form')
>>> form.actions
[<Action name="" submitted="True">,
<Action name="add_and_edit" submitted="False">]

The submitted action is available in the ``action`` parameter.

>>> form.action
<Action name="" submitted="True">

To call the form handler of the submitted action, we invoke the form's
call method.

>>> form()
add

To call the named form action, there must be a parameter in the
request which is a concatenation of the prefix and the form action
name. Accepted separation characters are '.' (dot), '_' (underscore)
and '-' (dash).

>>> request = Request(params=(
... ('tape_form-add_and_edit', ''),
... ('title', u'Motorcity Detroit USA Live'),))
>>> form = TapeAddForm(request=request, prefix='tape_form')
>>> form.actions
[<Action name="" submitted="False">,
<Action name="add_and_edit" submitted="True">]
>>> form()
add_and_edit

Data proxies
------------

We can bind a context object to a data object by using a proxy
object. This technique can be used to create edit or add-forms.

To illustrate this, let's define a content object. We'll hardcode
default values for simplicity.

>>> class Tape(object):
... artist = u'Bachman-Turner Overdrive'
... title = u'Four Wheel Drive'
... asin = 'B000001FL8'
... year = 1975
... playtime = 33.53

We can now create a data proxy for an instance of this class.

>>> tape = Tape()
>>> proxy = formapi.Proxy(tape)

With no further intervention, this data object acts as a proxy to read
and write attributes on the content object.

>>> proxy.title
u'Four Wheel Drive'
>>> proxy.title = u'Motorcity Detroit USA Live'
>>> tape.title
u'Motorcity Detroit USA Live'

If we want to have more control over this process, we can subclass and
define descriptors.

The following example defines custom behavior for the ``title``
attribute; the value is uppercased.

>>> class TapeProxy(formapi.Proxy):
... def get_title(self):
... return self.title
...
... def set_title(self, value):
... self.title = value.upper()
...
... title = property(get_title, set_title)
>>> proxy = TapeProxy(tape)

If we read and write to the ``title`` attribute of this proxy object,
the custom getter and setter functions are used.

>>> proxy.title = u'Motorcity Detroit USA Live'

As would be expected from a proxy, changes are actually made to the
underlying content object.

>>> tape.title
u'MOTORCITY DETROIT USA LIVE'

Saving form data
----------------

When instantiating a form, you can pass in a proxy object instead of
``data``. This binds the data object to the proxy, but it also allows
us to save the form data on the proxied object.

>>> form = TapeForm(proxy, request=request)
>>> form.data['title'] = u'Four Wheel Drive'

Assignment behaves logically.

>>> form.data['title']
u'Four Wheel Drive'

However, if we invoke the ``save`` action, changes take effect on the
proxied object.

>>> form.data.save()
>>> tape.title
u'FOUR WHEEL DRIVE'
Changelog
=========

0.5.3 (2012-11-23)
------------------

- Fixed an issue where a fields definition with a single entry would
get incorrectly marshalled when the corresponding data had multiple
entries.

0.5.2 (2012-11-19)
------------------

- Fixed an issue with `required` where the marshaller would not
correctly convert a value to the provided value type.


0.5.1 (2012-11-16)
------------------

- Type-checking has been removed from the marshalling code::

if not error and not isinstance(value, data_type):
error = True

This change was required to support "schema types" such as::

import re

match_email = re.compile(
r"^(\w&.%#$&'\*+-/=?^_`{}|~]+!)*[\w&.%#$&'"
r"\*+-/=?^_`{}|~]+@(([0-9a-z]([0-9a-z-]*[0-9a-z])"
r"?\.)+[a-z]{2,6}|([0-9]{1,3}\.){3}[0-9]{1,3})$",
re.IGNORECASE).match

class email(unicode):
def __new__(cls, string):
if match_email(string):
return string

raise ValueError(u"Not a valid e-mail address.")


0.5.0 (2010-05-28)
------------------

- Fixed ``Errors`` class to use the more obtuse ``__getattr__``
override; this fixes an issue where an attribute lookup of
``__class__`` would fail. [malthe]

- Added ``required`` decorator for field types; when we wrap a type
with this decorator, inputs that do not validate (even the trivial
input of the empty string) are given the input value as-is. Compare
this to an optional field (the default setting) where the empty
string will be interpreted as a non-input (unless it's a string type
or another type which will accept the empty string). [malthe]

- Add __contains__/has_key support to the Error class. [wichert]

0.4.2 (2009-09-14)
------------------

- Added ``any`` builtin fallback. [malthe]

0.4.1 (2009-07-31)
------------------

- Added defaultdict emulation class. [malthe]

0.4 (2009-07-29)
----------------

- The selected action, if any, is available in the ``action``
attribute of a form instance. [malthe]

- Even if form input does not validate, the input is available as-is
in the ``data`` dictionary. [malthe, rnix]

- Request parameters can now be provided directly as the ``params``
keyword argument. [malthe]

- Added ``get`` method to errors dictionary. [malthe]

- Errors can now be compared with each other to see if they are the
same. This makes it easier to test without doctest.

- Made the truth test for the errors object check just for messages in
itself or it's sub errors. This avoids having the errors object
saying it is true after accessing a key for which no error exists
(thus creating a new errors object). [jvloothuis]

- Changed the base class of errors from unicode to object. This makes
it behave like one would expect when printing etc. [jvloothuis]

0.3.2 (2009-03-09)
------------------

- Shedding unused dependency on 'zope.interface' [jvloothuis]

0.3.1 (2008-10-27)
------------------

- Make it possible to set `prefix` as class attribute. [malthe]

- Fixed issue where action parameters would not get set. [malthe]

0.3 (2008-10-27)
----------------

- Marshalled data is no longer applied when no parameters are
available from the request. [malthe]

- Made the `errors`-object subclass unicode instead of defaultdict and
implemented custom string representation function which concatenates
error messages. [malthe]

0.2 (2008-10-19)
----------------

- Created/improved the abilities for custom validation. [jvloothuis]

- Added form action support. [malthe]

- Reworked marshalling code to handle dynamic dictionary
keys. [malthe]

- Implemented form data object which facilities the form processing
flow from applying the request to committing changes to a context
object. [malthe]

- Integrated the converter into the ``form`` module. [seletz]

- Added ``ValidationErrors`` object, which evaluates to True if validation
errors occured. [seletz]

- Added ``unicode`` converter. [seletz]

- Added ``converter`` module to support converting and validating request
parameters sent by a form. [seletz]

- Added logic to allow registering and acquiring template API
components from templates. [malthe]

- Changed the Skin Template View to be a class, and added a minimal
interface ISkinTemplate to access the template path [seletz]

- Fixed a bug where we did not tear down the tests correctly [seletz]

- Fixed bug where the INewRequest event handler would call
templates when checking for their existence [seletz]

0.1 (2008-09-25)
----------------

- Initial release [malthe]

- Added support to dynamically register templates if they
are added to a registered template directory [seletz]