python “Bad operand type for abs ”

学的还很初级。想请问一下
1.如何看python提示的错误信息
2.这段代码哪里出错了。
谢谢～
报的错误是
raceback (most recent call last):
File "/Users/sharonxiao/Documents/howtodraw.py", line 26, in
draw_square()
File "/Users/sharonxiao/Documents/howtodraw.py", line 22, in draw_square
lara.circle("100")
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk/turtle.py", line 1892, in circle
steps = 1+int(min(11+abs(radius)/6.0, 59.0)*frac)
TypeError: bad operand type for abs(): 'str'

源码是
import turtle

def draw_square():
window=turtle.Screen()
window.bgcolor("white")

sharon= turtle.Turtle()
sharon.shape("circle")
sharon.color("green")
sharon.speed("2")
sharon.forward(200)
sharon.right(90)
sharon.forward(200)
sharon.right(90)
sharon.forward(200)
sharon.right(90)
sharon.forward(200)

lara=turtle.Turtle()
lara.shape("turtle")
lara.color("yellow")
lara.circle("100")

window.exitonclick()

lara.circle("100")这里引号去掉试试
错误信息说的是abs内错误的字符串类型

% 取模不能用浮点数， frequence 要转成整型来取模，小数位可以乘10后转整型来得到。