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1 #############################################################################
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2 #
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3 # Copyright (c) 2010 by Casey Duncan and contributors
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4 # All Rights Reserved.
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5 #
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6 # This software is subject to the provisions of the MIT License
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7 # A copy of the license should accompany this distribution.
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8 # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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9 # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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10 # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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11 #
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12 #############################################################################
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13 """Grease entities are useful as actionable, interactive
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14 game elements that are often visible to the player.
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15
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16 You might use entities to represent:
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17
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18 - Characters
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19 - Bullets
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20 - Particles
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21 - Pick-ups
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22 - Space Ships
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23 - Weapons
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24 - Trees
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25 - Planets
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26 - Explosions
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27
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28 See :ref:`an example entity class in the tutorial <tut-entity-example>`.
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29 """
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30
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31 __version__ = '$Id$'
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32
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33 __all__ = ('Entity', 'EntityComponentAccessor', 'ComponentEntitySet')
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34
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35
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36 class EntityMeta(type):
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37 """The entity metaclass enforces fixed slots of `entity_id` and `world`
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38 for all subclasses. This prevents accidental use of other entity instance
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39 attributes, which may not be saved.
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40
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41 Class attributes are not affected by this restriction, but subclasses
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42 should be careful not to cause name collisions with world components,
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43 which are exposed as entity attributes. Using a naming convention for
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44 class attributes, such as UPPER_CASE_WITH_UNDERSCORES is recommended to
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45 avoid name clashes.
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46
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47 Note as a result of this, entity subclasses are not allowed to define
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48 `__slots__`, and doing so will cause a `TypeError` to be raised.
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49 """
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50
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51 def __new__(cls, name, bases, clsdict):
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52 if '__slots__' in clsdict:
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53 raise TypeError('__slots__ may not be defined in Entity subclasses')
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54 clsdict['__slots__'] = ('world', 'entity_id')
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55 return type.__new__(cls, name, bases, clsdict)
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56
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57
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58 class Entity(object):
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59 """Base class for grease entities.
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60
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61 Entity objects themselves are merely identifiers within a :class:`grease.world.World`.
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62 They also provide a facade for convenient entity-wise access of component
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63 data. However, they do not contain any data themselves other than an
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64 entity id.
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65
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66 Entities must be instantiated in the context of a world. To instantiate an
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67 entity, you must pass the world as the first argument to the constructor.
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68 Subclasses that implement the :meth:`__init__()` method, must accept the world
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69 as their first argument (after ``self``). Other constructor arguments can be
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70 specified arbitarily by the subclass.
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71 """
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72 __metaclass__ = EntityMeta
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73
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74 def __new__(cls, world, *args, **kw):
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75 """Create a new entity and add it to the world"""
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76 entity = object.__new__(cls)
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77 entity.world = world
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78 entity.entity_id = world.new_entity_id()
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79 world.entities.add(entity)
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80 return entity
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81
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82 def __getattr__(self, name):
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83 """Return an :class:`EntityComponentAccessor` for this entity
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84 for the component named.
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85
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86 Example::
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87
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88 my_entity.movement
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89 """
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90 component = getattr(self.world.components, name)
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91 return EntityComponentAccessor(component, self)
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92
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93 def __setattr__(self, name, value):
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94 """Set the entity data in the named component for this entity.
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95 This sets the values of the component fields to the values of
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96 the matching attributes of the value provided. This value must
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97 have attributes for each of the component fields.
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98
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99 This allows you to easily copy component data from one entity
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100 to another.
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101
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102 Example::
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103
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104 my_entity.position = other_entity.position
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105 """
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106 if name in self.__class__.__slots__:
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107 super(Entity, self).__setattr__(name, value)
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108 else:
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109 component = getattr(self.world.components, name)
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110 component.set(self, value)
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111
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112 def __delattr__(self, name):
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113 """Remove this entity and its data from the component.
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114
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115 Example::
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116
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117 del my_entity.renderable
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118 """
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119 component = getattr(self.world.components, name)
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120 del component[self]
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121
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122 def __hash__(self):
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123 return self.entity_id
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124
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125 def __eq__(self, other):
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126 return self.world is other.world and self.entity_id == other.entity_id
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127
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128 def __repr__(self):
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129 return "<%s id: %s of %s %x>" % (
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130 self.__class__.__name__, self.entity_id,
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131 self.world.__class__.__name__, id(self.world))
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132
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133 def delete(self):
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134 """Delete the entity from its world. This removes all of its
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135 component data. If then entity has already been deleted,
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136 this call does nothing.
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137 """
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138 self.world.entities.discard(self)
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139
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140 @property
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141 def exists(self):
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142 """True if the entity still exists in the world"""
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143 return self in self.world.entities
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144
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145
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146 class EntityComponentAccessor(object):
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147 """A facade for accessing specific component data for a single entity.
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148 The implementation is lazy and does not actually access the component
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149 data until needed. If an attribute is set for a component that the
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150 entity is not yet a member of, it is automatically added to the
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151 component first.
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152
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153 :param component: The :class:`grease.Component` being accessed
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154 :param entity: The :class:`Entity` being accessed
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155 """
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156
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157 # beware, name mangling ahead. We want to avoid clashing with any
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158 # user-configured component field names
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159 __data = None
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160
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161 def __init__(self, component, entity):
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162 clsname = self.__class__.__name__
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163 self.__dict__['_%s__component' % clsname] = component
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164 self.__dict__['_%s__entity' % clsname] = entity
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165
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166 def __nonzero__(self):
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167 """The accessor is True if the entity is in the component,
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168 False if not, for convenient membership tests
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169 """
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170 return self.__entity in self.__component
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171
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172 def __getattr__(self, name):
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173 """Return the data for the specified field of the entity's component"""
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174 if self.__data is None:
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175 try:
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176 data = self.__component[self.__entity]
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177 except KeyError:
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178 raise AttributeError(name)
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179 clsname = self.__class__.__name__
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180 self.__dict__['_%s__data' % clsname] = data
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181 return getattr(self.__data, name)
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182
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183 def __setattr__(self, name, value):
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184 """Set the data for the specified field of the entity's component"""
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185 if self.__data is None:
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186 clsname = self.__class__.__name__
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187 if self.__entity in self.__component:
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188 self.__dict__['_%s__data' % clsname] = self.__component[self.__entity]
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189 else:
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190 self.__dict__['_%s__data' % clsname] = self.__component.set(self.__entity)
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191 setattr(self.__data, name, value)
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192
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193
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194 class ComponentEntitySet(set):
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195 """Set of entities in a component, can be queried by component fields"""
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196
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197 _component = None
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198
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199 def __init__(self, component, entities=()):
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200 self.__dict__['_component'] = component
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201 super(ComponentEntitySet, self).__init__(entities)
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202
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203 def __getattr__(self, name):
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204 if self._component is not None and name in self._component.fields:
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205 return self._component.fields[name].accessor(self)
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206 raise AttributeError(name)
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207
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208 def __setattr__(self, name, value):
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209 if self._component is not None and name in self._component.fields:
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210 self._component.fields[name].accessor(self).__set__(value)
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211 raise AttributeError(name)
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212
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