面向对象的Python编程

Question

Am trying to understand object oriented programming with python. Am new to programming. I have this class that is giving me an error I don't understand and I will be glad if anyone can throw more light on this for me:

class TimeIt(object):

    def __init__(self, name):
        self.name = name

    def test_one(self):
        print 'executed'

    def test_two(self, word):
        self.word = word
        i = getattr(self, 'test_one')
        for i in xrange(12):
            sleep(1)
            print 'hello, %s and %s:' % (self.word, self.name),
            i()

j = TimeIt('john')  
j.test_two('mike')

If I run this class I get 'int' object is not callable" TypeError

However, if I precede the i with self ( self.i ), it works.

class TimeIt(object):

    def __init__(self, name):
        self.name = name

    def test_one(self):
        print 'executed'

    def test_two(self, word):
        self.word = word
        self.i = getattr(self, 'test_one')
        for i in xrange(12):
            sleep(1)
            print 'hello, %s and %s:' % (self.word, self.name),
            self.i()

My question is, doesn't i = getattr(self, 'test_one') assign the test_one function to i ?
How come i() doesn't work?
Why does self.i() work?
Why is i an int (hence the 'int' object is not callable TypeError )?
That's a lot of questions. Thanks in advance

Answer 1

You're overwriting i within loop. When you're "preceding" i with self , you're creating different variable, which is not overwritten.

Answer 2

@SilentGhost is right on the money with his answer.

To illustrate, try chaning the test_two method to this:

def test_two(self, word):
    self.word = word
    i = getattr(self, 'test_one')
    for some_other_variable_besides_i in xrange(12):
        sleep(1)
        print 'hello, %s and %s:' % (self.word, self.name),
        i()

Your code overwrite the variable i (set as a method) within the for loop (see comments)

def test_two(self, word):
    self.word = word
    i = getattr(self, 'test_one')
    # i is now pointing to the method self.test_one
    for i in xrange(12):
        # now i is an int based on it being the variable name chosen for the loop on xrange
        sleep(1)
        print 'hello, %s and %s:' % (self.word, self.name),
        i()

In addition, you certainly don't need to assign the test_one method to a variable like i . Instead, you can just call the method replacing

i()

with

self.test_one()