157 lines
5.1 KiB
Python
157 lines
5.1 KiB
Python
import random
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import logging
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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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from xblock.fields import String, Scope, Dict
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DEFAULT = "_DEFAULT_GROUP"
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log = logging.getLogger(__name__)
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def group_from_value(groups, v):
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"""
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Given group: (('a', 0.3), ('b', 0.4), ('c', 0.3)) and random value v
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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 ABTestFields(object):
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group_portions = Dict(help="What proportions of students should go in each group", default={DEFAULT: 1}, scope=Scope.content)
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group_assignments = Dict(help="What group this user belongs to", scope=Scope.preferences, default={})
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group_content = Dict(help="What content to display to each group", scope=Scope.content, default={DEFAULT: []})
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experiment = String(help="Experiment that this A/B test belongs to", scope=Scope.content)
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has_children = True
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class ABTestModule(ABTestFields, 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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"""
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def __init__(self, *args, **kwargs):
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XModule.__init__(self, *args, **kwargs)
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if self.group is None:
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self.group = group_from_value(
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self.group_portions.items(),
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random.uniform(0, 1)
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)
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@property
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def group(self):
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return self.group_assignments.get(self.experiment)
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@group.setter
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def group(self, value):
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self.group_assignments[self.experiment] = value
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@group.deleter
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def group(self):
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del self.group_assignments[self.experiment]
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def get_child_descriptors(self):
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active_locations = set(self.group_content[self.group])
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return [desc for desc in self.descriptor.get_children() if desc.location.url() in active_locations]
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def displayable_items(self):
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# Most modules return "self" as the displayable_item. We never display ourself
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# (which is why we don't implement get_html). We only display our children.
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return self.get_children()
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# TODO (cpennington): Use Groups should be a first class object, rather than being
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# managed by ABTests
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class ABTestDescriptor(ABTestFields, RawDescriptor, XmlDescriptor):
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module_class = ABTestModule
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@classmethod
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def definition_from_xml(cls, xml_object, system):
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"""
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XML Format:
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<abtest experiment="experiment_name">
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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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experiment = xml_object.get('experiment')
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if experiment is None:
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raise InvalidDefinitionError(
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"ABTests must specify an experiment. Not found in:\n{xml}"
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.format(xml=etree.tostring(xml_object, pretty_print=True)))
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group_portions = {}
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group_content = {}
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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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group_portions[name] = float(group.get('portion', 0))
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child_content_urls = []
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for child in group:
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try:
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child_content_urls.append(system.process_xml(etree.tostring(child)).location.url())
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except:
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log.exception("Unable to load child when parsing ABTest. Continuing...")
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continue
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group_content[name] = child_content_urls
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children.extend(child_content_urls)
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default_portion = 1 - sum(
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portion for (name, portion) in group_portions.items()
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)
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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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group_portions[DEFAULT] = default_portion
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children.sort()
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return {
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'group_portions': group_portions,
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'group_content': group_content,
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}, children
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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.experiment)
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for name, group in self.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.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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def has_dynamic_children(self):
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return True
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