TypeError：int（）参数必须是字符串或数字，而不是'Binary'

Question

I'm working through http://blog.thedigitalcatonline.com/blog/2015/05/13/python-oop-tdd-example-part1/#.VxEEfjE2sdQ . I'm working through this iteratively. At this point I have the following Binary class:

class Binary:
    def __init__(self,value):
        self.value = str(value)
        if self.value[:2] == '0b':
            print('a binary!')
            self.value= int(self.value, base=2)
        elif self.value[:2] == '0x':
            print('a hex!')
            self.value= int(self.value, base=5)
        else:
            print(self.value)
        return None

I'm running through a suite of tests using pytest, including:

    def test_binary_init_hex():
        binary = Binary(0x6)
        assert int(binary) == 6
      E TypeError: int() argument must be a string or a number, not 'Binary'

    def test_binary_init_binstr():
        binary = Binary('0b110')
        assert int(binary) == 6
     E  TypeError: int() argument must be a string or a number, not 'Binary'

I don't understand this error. What am I doing wrong?

edit: heres the class produced by the blog author:

import collections

class Binary:
    def __init__(self, value=0):
        if isinstance(value, collections.Sequence):
            if len(value) > 2 and value[0:2] == '0b':
                self._value = int(value, base=2)
            elif len(value) > 2 and value[0:2] == '0x':
                self._value = int(value, base=16)
            else:
                self._value = int(''.join([str(i) for i in value]), base=2)
        else:
            try:
                self._value = int(value)
                if self._value < 0:
                    raise ValueError("Binary cannot accept negative numbers. Use SizedBinary instead")
            except ValueError:
                raise ValueError("Cannot convert value {} to Binary".format(value))

    def __int__(self):
        return self._value

Answer 1

The int function cannot deal with user defined classes unless you specify in the class how it should work. The __int__ (not init) function gives the built-in python int() function information regarding how your user defined class (in this case, Binary) should be converted to an int.

class Binary:
    ...your init here
    def __int__(self):
        return int(self.value) #assuming self.value is of type int

Then you should be able to do things like.

print int(Binary(0x3)) #should print 3

I might also suggest standardizing the input for the __init__ function and the value of self.value . Currently, it can accept either a string (eg '0b011' or a 0x3 ) or an int. Why not just always make it accept a string as input and always keep self.value as an int.