Elements¶
Elements describe the possible fields of a form; their names, structure, Python types and rules for validation. A typical schema consists of at least one container type and one or more scalar types:
from flatland import Dict, String
SearchSchema = Dict.named('search').of(String.named(u'keywords'))
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FieldSchemas are a bit like Python class definitions: they need be defined only once and don’t do much on their own. FieldSchema.create_element() produces Elements; closely related objects that hold and manipulate form data. Much like a Python class, a single FieldSchema may produce an unlimited number of Element instances.
>>> form = SearchSchema({u'keywords': u'foo bar baz'})
>>> form.value
{u'keywords': u'foo bar baz'}
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FieldSchema instances may be freely composed and shared among many containers.
>>> from flatland import List
>>> ComposedSchema = Dict.of(SearchSchema,
... List.named(u'many_searches').of(SearchSchema))
>>> form = ComposedSchema()
>>> sorted(form.value.keys())
[u'many_searches', u'search']
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Elements can be supplied to template environments and used to great effect there: elements contain all of the information needed to display or redisplay a HTML form field, including errors specific to a field.
The u, x, xa and el() members are especially useful in templates and have shortened names to help preserve your sanity when used in markup.
Element¶
- class Element(value=Unspecified, **kw)¶
Base class for form fields.
A data node that stores a Python and a text value plus added state.
Instance Attributes
- parent¶
An owning element, or None if element is topmost or not a member of a hierarchy.
- valid¶
- errors¶
A list of validation error messages.
- warnings¶
A list of validation warning messages.
Members
- name = None¶
The Unicode name of the element.
- optional = False¶
If True, validate() with return True if no value has been set.
validators are not called for optional, empty elements.
- validators = ()¶
A sequence of validators, invoked by validate().
See Validation.
- default = None¶
The default value of this element.
- default_factory = None¶
A callable to generate default element values. Passed an element.
default_factory will be used preferentially over default.
- ugettext = None¶
If set, provides translation support to validation messages.
- ungettext = None¶
If set, provides translation support to validation messages.
- value = None¶
The element’s native Python value.
Only validation routines should write this attribute directly: use set() to update the element’s value.
- raw = Unset¶
The element’s raw, unadapted value from input.
- u = u''¶
A Unicode representation of the element’s value.
As in value, writing directly to this attribute should be restricted to validation routines.
- properties = {}¶
A mapping of arbitrary data associated with the element.
- classmethod named(name)¶
Return a class with name = name
Parameters: name – a string or None. str will be converted to unicode. Returns: a new class
- classmethod using(**overrides)¶
Return a class with attributes set from **overrides.
Parameters: **overrides – new values for any attributes already present on the class. A TypeError is raised for unknown attributes. Returns: a new class
- classmethod validated_by(*validators)¶
Return a class with validators set to *validators.
Parameters: *validators – one or more validator functions, replacing any validators present on the class. Returns: a new class
- classmethod including_validators(*validators, **kw)¶
Return a class with additional *validators.
Parameters: - *validators – one or more validator functions
- position – defaults to -1. By default, additional validators are placed after existing validators. Use 0 for before, or any other list index to splice in validators at that point.
Returns: a new class
- classmethod with_properties(*iterable, **properties)¶
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- validate_element(element, state, descending)¶
Assess the validity of an element.
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this method is dead. Evaluate docstring for good bits that should be elsewhere.
Parameters: - element – an Element
- state – may be None, an optional value of supplied to element.validate
- descending – a boolean, True the first time the element has been seen in this run, False the next
Returns: boolean; a truth value or None
The Element.validate() process visits each element in the tree twice: once heading down the tree, breadth-first, and again heading back up in the reverse direction. Scalar fields will typically validate on the first pass, and containers on the second.
Return no value or None to pass, accepting the element as presumptively valid.
Exceptions raised by validate_element() will not be caught by Element.validate().
Directly modifying and normalizing Element.value and Element.u within a validation routine is acceptable.
The standard implementation of validate_element is:
- If element.is_empty and self.optional, return True.
- If self.validators is empty and element.is_empty, return False.
- If self.validators is empty and not element.is_empty, return True.
- Iterate through self.validators, calling each member with (element, state). If one returns a false value, stop iterating and return False immediately.
- Otherwise return True.
- classmethod from_flat(pairs, **kw)¶
Return a new element with its value initialized from pairs.
Parameters: **kw – passed through to the element_type. This is a convenience constructor for:
element = cls(**kw) element.set_flat(pairs)
- classmethod from_defaults(**kw)¶
Return a new element with its value initialized from field defaults.
Parameters: **kw – passed through to the element_type. This is a convenience constructor for:
element = cls(**kw) element.set_default()
- all_valid¶
True if this element and all children are valid.
- root¶
The top-most parent of the element.
- parents¶
An iterator of all parent elements.
- path¶
An iterator of all elements from root to the Element, inclusive.
- children¶
An iterator of immediate child elements.
- all_children¶
An iterator of all child elements, breadth-first.
- fq_name(sep=u'.')¶
Return the fully qualified path name of the element.
Returns a sep-separated string of el() compatible element indexes starting from the Element.root (.) down to the element.
>>> from flatland import Dict, Integer >>> Point = Dict.named(u'point').of(Integer.named(u'x'), ... Integer.named(u'y')) >>> p = Point(dict(x=10, y=20)) >>> p.name u'point' >>> p.fq_name() u'.' >>> p['x'].name u'x' >>> p['x'].fq_name() u'.x'
The index used in a path may not be the name of the element. For example, sequence members are referenced by their numeric index.
>>> from flatland import List, String >>> Addresses = List.named('addresses').of(String.named('address')) >>> form = Addresses([u'uptown', u'downtown']) >>> form.name u'addresses' >>> form.fq_name() u'.' >>> form[0].name u'address' >>> form[0].fq_name() u'.0'
- find(path, single=False, strict=True)¶
Find child elements by string path.
Parameters: - path – a /-separated string specifying elements to select, such as ‘child/grandchild/great grandchild’. Relative & absolute paths are supported, as well as container expansion. See Path Lookups.
- single – if true, return a scalar result rather than a list of elements. If no elements match path, None is returned. If multiple elements match, a LookupError is raised. If multiple elements are found and strict is false, an unspecified element from the result set is returned.
- strict – defaults to True. If path specifies children or sequence indexes that do not exist, a LookupError is raised.
Returns: a list of Element instances, an Element if single is true, or raises LookupError.
>>> cities = form.find('/contact/addresses[:]/city') >>> [el.value for el in cities] [u'Kingsport', u'Dunwich'] >>> form.find('/contact/name', single=True) <String u'name'; value=u'Obed Marsh'>
- el(path, sep=u'.')¶
Find a child element by string path.
Parameters: - path – a sep-separated string of element names, or an iterable of names
- sep – optional, a string separator used to parse path
Returns: an Element or raises KeyError.
>>> first_address = form.el('contact.addresses.0') >>> first_address.el('street1') <String u'street1'; value=None>
Given a relative path as above, el() searches for a matching path among the element’s children.
If path begins with sep, the path is considered fully qualified and the search is resolved from the Element.root. The leading sep will always match the root node, regardless of its name.
>>> form.el('.contact.addresses.0.city') <String u'city'; value=None> >>> first_address.el('.contact.addresses.0.city') <String u'city'; value=None>
- add_error(message)¶
Register an error message on this element, ignoring duplicates.
- add_warning(message)¶
Register a warning message on this element, ignoring duplicates.
- flattened_name(sep=u'_')¶
Return the element’s complete flattened name as a string.
Joins this element’s path with sep and returns the fully qualified, flattened name. Encodes all Container and other structures into a single string.
Example:
>>> import flatland >>> form = flatland.List('addresses', ... flatland.String('address')) >>> element = form() >>> element.set([u'uptown', u'downtown']) >>> element.el('0').value u'uptown' >>> element.el('0').flattened_name() u'addresses_0_address'
- flatten(sep=u'_', value=<operator.attrgetter object at 0x3c0df90>)¶
Export an element hierarchy as a flat sequence of key, value pairs.
Parameters: - sep – a string, will join together element names.
- value – a 1-arg callable called once for each element. Defaults to a callable that returns the u of each element.
Encodes the element hierarchy in a sep-separated name string, paired with any representation of the element you like. The default is the Unicode value of the element, and the output of the default flatten() can be round-tripped with set_flat().
Given a simple form with a string field and a nested dictionary:
>>> from flatland import Dict, String >>> class Nested(Form): ... contact = Dict.of(String.named(u'name'), ... Dict.named(u'address'). ... of(String.named(u'email'))) ... >>> element = Nested() >>> element.flatten() [(u'contact_name', u''), (u'contact_address_email', u'')]
The value of each pair can be customized with the value callable:
>>> element.flatten(value=operator.attrgetter('u')) [(u'contact_name', u''), (u'contact_address_email', u'')] >>> element.flatten(value=lambda el: el.value) [(u'contact_name', None), (u'contact_address_email', None)]
Solo elements will return a sequence containing a single pair:
>>> element['name'].flatten() [(u'contact_name', u'')]
- set(value)¶
Assign the native and Unicode value.
Attempts to adapt the given value and assigns this element’s value and u attributes in tandem. Returns True if the adaptation was successful.
If adaptation succeeds, value will contain the adapted native value and u will contain a Unicode serialized version of it. A native value of None will be represented as u’’ in u.
If adaptation fails, value will be None and u will contain unicode(value) or u'' for None.
>>> from flatland import Integer >>> el = Integer() >>> el.u, el.value (u'', None)
>>> el.set('123') True >>> el.u, el.value (u'123', 123)
>>> el.set(456) True >>> el.u, el.value (u'456', 456)
>>> el.set('abc') False >>> el.u, el.value (u'abc', None)
>>> el.set(None) True >>> el.u, el.value (u'', None)
- set_flat(pairs, sep=u'_')¶
Set element values from pairs, expanding the element tree as needed.
Given a sequence of name/value tuples or a dict, build out a structured tree of value elements.
- set_default()¶
set() the element to the schema default.
- is_empty¶
True if the element has no value.
- validate(state=None, recurse=True)¶
Assess the validity of this element and its children.
Parameters: - state – optional, will be passed unchanged to all validator callables.
- recurse – if False, do not validate children.
Returns: True or False.
Iterates through this element and all of its children, invoking each element’s schema.validate_element(). Each element will be visited twice: once heading down the tree, breadth-first, and again heading back up in reverse order.
Returns True if all validations pass, False if one or more fail.
- default_value¶
A calculated “default” value.
If default_factory is present, it will be called with the element as a single positional argument. The result of the call will be returned.
Otherwise, returns default.
When comparing an element’s value to its default value, use this property in the comparison.
