124 lines
4.2 KiB
Python
124 lines
4.2 KiB
Python
import json
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import random
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from lxml import etree
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from xmodule.x_module import XModule
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from xmodule.raw_module import RawDescriptor
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from xmodule.xml_module import XmlDescriptor
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from xmodule.exceptions import InvalidDefinitionError
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DEFAULT = "_DEFAULT_GROUP"
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def group_from_value(groups, v):
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''' Given group: (('a',0.3),('b',0.4),('c',0.3)) And random value
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in [0,1], return the associated group (in the above case, return
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'a' if v<0.3, 'b' if 0.3<=v<0.7, and 'c' if v>0.7
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'''
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sum = 0
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for (g, p) in groups:
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sum = sum + p
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if sum > v:
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return g
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# Round off errors might cause us to run to the end of the list
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# If the do, return the last element
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return g
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class ABTestModule(XModule):
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"""
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Implements an A/B test with an aribtrary number of competing groups
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Format:
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<abtest>
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<group name="a" portion=".1"><contenta/></group>
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<group name="b" portion=".2"><contentb/></group>
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<default><contentdefault/></default>
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</abtest>
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"""
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def __init__(self, system, location, definition, instance_state=None, shared_state=None, **kwargs):
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XModule.__init__(self, system, location, definition, instance_state, shared_state, **kwargs)
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if shared_state is None:
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self.group = group_from_value(
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self.definition['data']['group_portions'].items(),
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random.uniform(0, 1)
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)
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else:
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shared_state = json.loads(shared_state)
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self.group = shared_state['group']
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def get_shared_state(self):
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return json.dumps({'group': self.group})
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def displayable_items(self):
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return [self.system.get_module(child)
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for child
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in self.definition['data']['group_content'][self.group]]
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class ABTestDescriptor(RawDescriptor, XmlDescriptor):
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module_class = ABTestModule
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def __init__(self, system, definition=None, **kwargs):
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kwargs['shared_state_key'] = definition['data']['experiment']
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RawDescriptor.__init__(self, system, definition, **kwargs)
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@classmethod
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def definition_from_xml(cls, xml_object, system):
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experiment = xml_object.get('experiment')
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if experiment is None:
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raise InvalidDefinitionError("ABTests must specify an experiment. Not found in:\n{xml}".format(xml=etree.tostring(xml_object, pretty_print=True)))
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definition = {
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'data': {
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'experiment': experiment,
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'group_portions': {},
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'group_content': {DEFAULT: []},
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},
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'children': []}
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for group in xml_object:
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if group.tag == 'default':
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name = DEFAULT
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else:
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name = group.get('name')
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definition['data']['group_portions'][name] = float(group.get('portion', 0))
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child_content_urls = [
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system.process_xml(etree.tostring(child)).location.url()
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for child in group
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]
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definition['data']['group_content'][name] = child_content_urls
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definition['children'].extend(child_content_urls)
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default_portion = 1 - sum(portion for (name, portion) in definition['data']['group_portions'].items())
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if default_portion < 0:
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raise InvalidDefinitionError("ABTest portions must add up to less than or equal to 1")
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definition['data']['group_portions'][DEFAULT] = default_portion
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return definition
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def definition_to_xml(self, resource_fs):
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xml_object = etree.Element('abtest')
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xml_object.set('experiment', self.definition['data']['experiment'])
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for name, group in self.definition['data']['group_content'].items():
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if name == DEFAULT:
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group_elem = etree.SubElement(xml_object, 'default')
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else:
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group_elem = etree.SubElement(xml_object, 'group', attrib={
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'portion': str(self.definition['data']['group_portions'][name]),
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'name': name,
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})
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for child_loc in group:
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child = self.system.load_item(child_loc)
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group_elem.append(etree.fromstring(child.export_to_xml(resource_fs)))
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return xml_object
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