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class Preparer(object):
"""
A plain preparation object which just passes through data.
It also is relevant as the protocol subclasses should implement to work with
Restless.
"""
def __init__(self):
super(Preparer, self).__init__()
def prepare(self, data):
"""
Handles actually transforming the data.
By default, this does nothing & simply returns the data passed to it.
"""
return data
class FieldsPreparer(Preparer):
"""
A more complex preparation object, this will return a given set of fields.
This takes a ``fields`` parameter, which should be a dictionary of
keys (fieldnames to expose to the user) & values (a dotted lookup path to
the desired attribute/key on the object).
Example::
preparer = FieldsPreparer(fields={
# ``user`` is the key the client will see.
# ``author.pk`` is the dotted path lookup ``FieldsPreparer``
# will traverse on the data to return a value.
'user': 'author.pk',
})
"""
def __init__(self, fields):
super(FieldsPreparer, self).__init__()
self.fields = fields
def prepare(self, data):
"""
Handles transforming the provided data into the fielded data that should
be exposed to the end user.
Uses the ``lookup_data`` method to traverse dotted paths.
Returns a dictionary of data as the response.
"""
result = {}
if not self.fields:
# No fields specified. Serialize everything.
return data
for fieldname, lookup in self.fields.items():
result[fieldname] = self.lookup_data(lookup, data)
return result
def lookup_data(self, lookup, data):
"""
Given a lookup string, attempts to descend through nested data looking for
the value.
Can work with either dictionary-alikes or objects (or any combination of
those).
Lookups should be a string. If it is a dotted path, it will be split on
``.`` & it will traverse through to find the final value. If not, it will
simply attempt to find either a key or attribute of that name & return it.
Example::
>>> data = {
... 'type': 'message',
... 'greeting': {
... 'en': 'hello',
... 'fr': 'bonjour',
... 'es': 'hola',
... },
... 'person': Person(
... name='daniel'
... )
... }
>>> lookup_data('type', data)
'message'
>>> lookup_data('greeting.en', data)
'hello'
>>> lookup_data('person.name', data)
'daniel'
"""
value = data
parts = lookup.split('.')
if not parts or not parts[0]:
return value
part = parts[0]
remaining_lookup = '.'.join(parts[1:])
if hasattr(data, 'keys') and hasattr(data, '__getitem__'):
# Dictionary enough for us.
value = data[part]
else:
# Assume it's an object.
value = getattr(data, part)
if not remaining_lookup:
return value
# There's more to lookup, so dive in recursively.
return self.lookup_data(remaining_lookup, value)
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