mirror of
https://github.com/encode/django-rest-framework.git
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299 lines
9.2 KiB
Python
299 lines
9.2 KiB
Python
"""
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Customizable serialization.
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"""
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from django.db import models
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from django.db.models.query import QuerySet
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from django.utils.encoding import smart_unicode, is_protected_type, smart_str
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import inspect
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import types
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# We register serializer classes, so that we can refer to them by their
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# class names, if there are cyclical serialization heirachys.
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_serializers = {}
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def _field_to_tuple(field):
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"""
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Convert an item in the `fields` attribute into a 2-tuple.
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"""
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if isinstance(field, (tuple, list)):
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return (field[0], field[1])
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return (field, None)
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def _fields_to_list(fields):
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"""
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Return a list of field names.
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"""
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return [_field_to_tuple(field)[0] for field in fields or ()]
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def _fields_to_dict(fields):
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"""
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Return a `dict` of field name -> None, or tuple of fields, or Serializer class
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"""
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return dict([_field_to_tuple(field) for field in fields or ()])
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class _SkipField(Exception):
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"""
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Signals that a serialized field should be ignored.
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We use this mechanism as the default behavior for ensuring
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that we don't infinitely recurse when dealing with nested data.
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"""
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pass
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class _RegisterSerializer(type):
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"""
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Metaclass to register serializers.
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"""
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def __new__(cls, name, bases, attrs):
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# Build the class and register it.
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ret = super(_RegisterSerializer, cls).__new__(cls, name, bases, attrs)
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_serializers[name] = ret
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return ret
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class Serializer(object):
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"""
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Converts python objects into plain old native types suitable for
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serialization. In particular it handles models and querysets.
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The output format is specified by setting a number of attributes
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on the class.
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You may also override any of the serialization methods, to provide
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for more flexible behavior.
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Valid output types include anything that may be directly rendered into
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json, xml etc...
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"""
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__metaclass__ = _RegisterSerializer
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fields = ()
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"""
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Specify the fields to be serialized on a model or dict.
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Overrides `include` and `exclude`.
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"""
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include = ()
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"""
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Fields to add to the default set to be serialized on a model/dict.
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"""
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exclude = ()
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"""
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Fields to remove from the default set to be serialized on a model/dict.
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"""
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rename = {}
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"""
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A dict of key->name to use for the field keys.
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"""
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related_serializer = None
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"""
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The default serializer class to use for any related models.
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"""
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depth = None
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"""
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The maximum depth to serialize to, or `None`.
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"""
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def __init__(self, depth=None, stack=[], **kwargs):
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if depth is not None:
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self.depth = depth
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self.stack = stack
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def get_fields(self, obj):
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"""
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Return the set of field names/keys to use for a model instance/dict.
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"""
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fields = self.fields
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# If `fields` is not set, we use the default fields and modify
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# them with `include` and `exclude`
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if not fields:
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default = self.get_default_fields(obj)
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include = self.include or ()
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exclude = self.exclude or ()
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fields = set(default + list(include)) - set(exclude)
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else:
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fields = _fields_to_list(self.fields)
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return fields
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def get_default_fields(self, obj):
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"""
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Return the default list of field names/keys for a model instance/dict.
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These are used if `fields` is not given.
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"""
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if isinstance(obj, models.Model):
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opts = obj._meta
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return [field.name for field in opts.fields + opts.many_to_many]
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else:
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return obj.keys()
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def get_related_serializer(self, key):
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info = _fields_to_dict(self.fields).get(key, None)
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# If an element in `fields` is a 2-tuple of (str, tuple)
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# then the second element of the tuple is the fields to
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# set on the related serializer
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if isinstance(info, (list, tuple)):
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class OnTheFlySerializer(self.__class__):
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fields = info
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return OnTheFlySerializer
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# If an element in `fields` is a 2-tuple of (str, Serializer)
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# then the second element of the tuple is the Serializer
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# class to use for that field.
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elif isinstance(info, type) and issubclass(info, Serializer):
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return info
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# If an element in `fields` is a 2-tuple of (str, str)
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# then the second element of the tuple is the name of the Serializer
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# class to use for that field.
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#
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# Black magic to deal with cyclical Serializer dependancies.
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# Similar to what Django does for cyclically related models.
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elif isinstance(info, str) and info in _serializers:
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return _serializers[info]
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# Otherwise use `related_serializer` or fall back to `Serializer`
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return getattr(self, 'related_serializer') or Serializer
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def serialize_key(self, key):
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"""
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Keys serialize to their string value,
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unless they exist in the `rename` dict.
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"""
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return self.rename.get(smart_str(key), smart_str(key))
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def serialize_val(self, key, obj):
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"""
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Convert a model field or dict value into a serializable representation.
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"""
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related_serializer = self.get_related_serializer(key)
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if self.depth is None:
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depth = None
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elif self.depth <= 0:
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return self.serialize_max_depth(obj)
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else:
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depth = self.depth - 1
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if any([obj is elem for elem in self.stack]):
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return self.serialize_recursion(obj)
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else:
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stack = self.stack[:]
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stack.append(obj)
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return related_serializer(depth=depth, stack=stack).serialize(obj)
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def serialize_max_depth(self, obj):
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"""
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Determine how objects should be serialized once `depth` is exceeded.
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The default behavior is to ignore the field.
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"""
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raise _SkipField
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def serialize_recursion(self, obj):
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"""
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Determine how objects should be serialized if recursion occurs.
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The default behavior is to ignore the field.
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"""
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raise _SkipField
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def serialize_model(self, instance):
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"""
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Given a model instance or dict, serialize it to a dict..
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"""
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data = {}
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fields = self.get_fields(instance)
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# serialize each required field
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for fname in fields:
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try:
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# we first check for a method 'fname' on self,
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# 'fname's signature must be 'def fname(self, instance)'
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meth = getattr(self, fname, None)
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if (inspect.ismethod(meth) and
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len(inspect.getargspec(meth)[0]) == 2):
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obj = meth(instance)
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elif hasattr(instance, '__contains__') and fname in instance:
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# then check for a key 'fname' on the instance
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obj = instance[fname]
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elif hasattr(instance, smart_str(fname)):
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# finally check for an attribute 'fname' on the instance
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obj = getattr(instance, fname)
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else:
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continue
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key = self.serialize_key(fname)
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val = self.serialize_val(fname, obj)
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data[key] = val
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except _SkipField:
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pass
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return data
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def serialize_iter(self, obj):
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"""
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Convert iterables into a serializable representation.
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"""
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return [self.serialize(item) for item in obj]
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def serialize_func(self, obj):
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"""
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Convert no-arg methods and functions into a serializable representation.
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"""
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return self.serialize(obj())
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def serialize_manager(self, obj):
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"""
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Convert a model manager into a serializable representation.
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"""
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return self.serialize_iter(obj.all())
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def serialize_fallback(self, obj):
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"""
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Convert any unhandled object into a serializable representation.
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"""
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return smart_unicode(obj, strings_only=True)
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def serialize(self, obj):
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"""
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Convert any object into a serializable representation.
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"""
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if isinstance(obj, (dict, models.Model)):
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# Model instances & dictionaries
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return self.serialize_model(obj)
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elif isinstance(obj, (tuple, list, set, QuerySet, types.GeneratorType)):
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# basic iterables
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return self.serialize_iter(obj)
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elif isinstance(obj, models.Manager):
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# Manager objects
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return self.serialize_manager(obj)
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elif inspect.isfunction(obj) and not inspect.getargspec(obj)[0]:
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# function with no args
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return self.serialize_func(obj)
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elif inspect.ismethod(obj) and len(inspect.getargspec(obj)[0]) <= 1:
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# bound method
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return self.serialize_func(obj)
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# Protected types are passed through as is.
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# (i.e. Primitives like None, numbers, dates, and Decimals.)
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if is_protected_type(obj):
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return obj
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# All other values are converted to string.
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return self.serialize_fallback(obj)
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