Instance has no attribute _pi

Question

I'm trying to make a Python module like this:

class square:
    def _init_(self):
        self._length = 0
        self._perimeter = 0
        self._area = 0
    def setLength(self, length):
        self._length = float(length)
        self._perimeter = 0
        self._area = 0
    def getLength(self):
        return self._length
    def getPerimeter(self):
        if self._perimeter == 0:
            self._perimeter = float(self._length * 4)
        return self._perimeter
    def getArea(self):
        if self._area == 0:
            self._area = float(self._length * self._length)
        return self._area
class rectangle:
    def _init_(self):
        self._length = 0
        self._width = 0
        self._perimeter = 0
        self._area = 0
    def setLength(self, length):
        self._length = float(length)
        self._perimeter = 0
        self._area = 0
    def getLength(self):
        return self._length
    def setWidth(self, width):
        self._width = float(width)
        self._perimeter = 0
        self._area = 0
    def getWidth(self):
        return self._width
    def getPerimeter(self):
        if self._perimeter == 0:
            perim1 = float(self._length * 2)
            perim2 = float(self._width * 2)
            self._perimeter = float(perim1 + perim2)
        return self._perimeter
    def getArea(self):
        if self._area == 0:
            self._area = float(self._length * self._width)
        return self._area
class circle:
    def _init_(self):
        self._radius = 0
        self._diameter = 0
        self._circumference = 0
        self._pi = 3.14159265
    def setRadius(self, radius):
        self._radius = float(radius)
        self._diameter = float(self._radius * 2)
        self._circumference = 0
    def setDiameter(self, diameter):
        self._diameter = float(diameter)
        self._radius = float(self._diameter / 2)
        self._circumference = 0
    def getRadius(self):
        return self._radius
    def getDiameter(self):
        return self._diameter
    def getPi(self):
        return self._pi
    def getCircumference(self):
        if self._circumference == 0:
            self._circumference = float(self._diameter * self._pi)
        return self._circumference
class triangle:
    def _init_(self):
        self._side = []
        self._side[0] = 0
        self._side[1] = 0
        self._side[2] = 0
        self._side[3] = 0
        self._angle = []
        self._angle[0] = 0
        self._angle[1] = 0
        self._angle[2] = 0
        self._angle[3] = 0
        self._perimeter = 0
        self._area = 0
    def setSide(self, side, length):
        self._side[side] = float(length)
    def getSide(self, side):
        return self._side[side]
    def getPerimeter(self):
        if self._perimeter == 0:
            self._perimeter = side[1] + side[2] + side[3]
        return self._perimeter
    def setAngle(self, angle, measure):
        self._angle[angle] = float(measure)
    def getAngle(self, angle):
        if self._angle[angle] == 0:
            if angle == 1:
                angle1 = self._angle[2]
                angle2 = self._angle[3]
            elif angle == 2:
                angle1 = self._angle[1]
                angle2 = self._angle[3]
            elif angle == 3:
                angle1 = self._angle[1]
                angle2 = self._angle[2]
            anglet = angle1 + angle2
            angler = float(180) - anglet
            self._angle[angle] = angler
        return self.angle[angle]

It's part of a package named Mathworks. The calling code is this:

import mathworks as mw
mycircle = mw.shapes.circle()
mycircle.setDiameter(5)
circum = mycircle.getCircumference()
print circim

When I try two run the second module, I get this:

Traceback (most recent call last):
  File "<string>", line 254, in run_nodebug
  File "<module1>", line 21, in <module>
  File "<module1>", line 17, in main
  File "C:\Python27\lib\site-packages\mathworks\shapes.py", line 70, in getCircumference
    self._circumference = float(self._diameter * self._pi)
AttributeError: circle instance has no attribute '_pi'

What's wrong? It works if I replace self._pi with 3.14159265, but I need it to work the other way.

Answer 1

You didn't name your initializers correctly, it needs double underscores on either end:

def __init__(self):

You need to correct that for all your classes.

Because you didn't name them correctly, they are not being run when you create an instance of your classes.

Next problem you'll run into is your triangle initializer; you cannot address indexes in an empty list. Create the whole list in one go instead:

def __init__(self):
    self._side = [0, 0, 0, 0]
    self._angle = [0, 0, 0, 0]
    self._perimeter = 0
    self._area = 0