python中的TypeError错误解决办法

新手在学习python时候，会遇到很多的坑，下面来具体说说其中一个。

在使用python编写面向对象的程序时，新手可能遇到TypeError: this constructor takes no arguments这个错误。

例如下面的程序：

class Ball:
      def _init_(self,color,size,direction):
            self.color=color
            self.size=size
            self.direction=direction

      def bounce(self):
            if self.direction=="down":
                  self.direction="up"

myBall=Ball("red","small","down")
print "I just created a ball."
print "My ball is",myBall.size
print "My ball is",myBall.color
print "My ball's direction is",myBall.direction
print "Now I'm going to bounce the ball"
print
myBall.bounce()
print "Now the ball's direction is",myBall.direction

运行会报错：

======================= RESTART: H:pythonounce1.py =======================

Traceback (most recent call last):
  File "H:pythonounce1.py", line 11, in <module>
    myBall=Ball("red","small","down")
TypeError: this constructor takes no arguments

出错原因是，在python中构造函数书写格式是__init__，而不是_init_，即在init两侧都是双下划线，不是单下划线。

修改后如下：

class Ball:
      def __init__(self,color,size,direction):
            self.color=color
            self.size=size
            self.direction=direction

      def bounce(self):
            if self.direction=="down":
                  self.direction="up"

myBall=Ball("red","small","down")
print "I just created a ball."
print "My ball is",myBall.size
print "My ball is",myBall.color
print "My ball's direction is",myBall.direction
print "Now I'm going to bounce the ball"
print
myBall.bounce()
print "Now the ball's direction is",myBall.direction

这是正确的运行结果：

======================= RESTART: H:pythonounce1.py =======================
I just created a ball.
My ball is small
My ball is red
My ball's direction is down
Now I'm going to bounce the ball

Now the ball's direction is up