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# shapes.py
#
# A sample program showing how parse actions can convert parsed
# strings into a data type or object.
#
# Copyright 2012, 2019 Paul T. McGuire
#
# define class hierarchy of Shape classes, with polymorphic area method
class Shape:
def __init__(self, tokens):
self.__dict__.update(tokens.asDict())
def area(self):
raise NotImplemented()
def __str__(self):
return "<{}>: {}".format(self.__class__.__name__, vars(self))
class Square(Shape):
def area(self):
return self.side ** 2
class Rectangle(Shape):
def area(self):
return self.width * self.height
class Circle(Shape):
def area(self):
return 3.14159 * self.radius ** 2
import pyparsing as pp
ppc = pp.pyparsing_common
# use pyparsing-defined numeric expression that converts all parsed
# numeric values as floats
number = ppc.fnumber()
# Shape expressions:
# square : S <centerx> <centery> <side>
# rectangle: R <centerx> <centery> <width> <height>
# circle : C <centerx> <centery> <diameter>
squareDefn = "S" + number("centerx") + number("centery") + number("side")
rectDefn = (
"R" + number("centerx") + number("centery") + number("width") + number("height")
)
circleDefn = "C" + number("centerx") + number("centery") + number("diameter")
squareDefn.setParseAction(Square)
rectDefn.setParseAction(Rectangle)
def computeRadius(tokens):
tokens["radius"] = tokens.diameter / 2.0
circleDefn.setParseAction(computeRadius, Circle)
shapeExpr = squareDefn | rectDefn | circleDefn
tests = """\
C 0 0 100
R 10 10 20 50
S -1 5 10""".splitlines()
for t in tests:
shape = shapeExpr.parseString(t)[0]
print(shape)
print("Area:", shape.area())
print()
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