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expression.py
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expression.py
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from zope.interface import implementer, Interface, Attribute
from zope.interface.verify import verifyObject
"""SLIDE_START: define_interface"""
class IExpressionNode(Interface):
left = Attribute("The left child of this expression.")
right = Attribute("The right child of this expression.")
def evaluate():
"""Evaluate this expression"""
"""SLIDE_END: define_interface"""
"""SLIDE_START: addition_expression_node"""
@implementer(IExpressionNode)
class AdditionExpressionNode(object):
def __init__(self, left, right):
self.left = left
self.right = right
def evaluate(self):
return self.left.evaluate() + self.right.evaluate()
"""SLIDE_END: addition_expression_node"""
@implementer(IExpressionNode)
class IntegerExpressionNode(object):
left = None
right = None
def __init__(self, value):
self.value = value
def evaluate(self):
return self.value
@implementer(IExpressionNode)
class BrokenIntegerExpressionNode(object):
def __init__(self, value):
self.value = value
def evaluate(self):
return self.value
"""SLIDE_START: validate_addition_node"""
def validate_addition_node():
five = IntegerExpressionNode(5)
three = IntegerExpressionNode(3)
eight = AdditionExpressionNode(five, three)
IExpressionNode.implementedBy(AdditionExpressionNode)
IExpressionNode.providedBy(eight)
verifyObject(IExpressionNode, eight)
"""SLIDE_END: validate_addition_node"""
def validate_integer_node():
IExpressionNode.implementedBy(IntegerExpressionNode)
eight = IntegerExpressionNode(8)
IExpressionNode.providedBy(eight)
verifyObject(IExpressionNode, eight)
def validate_broken_integer_node():
IExpressionNode.implementedBy(BrokenIntegerExpressionNode)
eight = BrokenIntegerExpressionNode(8)
IExpressionNode.providedBy(eight)
verifyObject(IExpressionNode, eight)