[Tutor] Is this correct?

[Kent Johnson]

Hoffmann wrote:

> class Time:
> 	def __init__(self, hours = 0, minutes = 0, seconds =
> 0):
> 		self.hours = hours
> 		self.minutes = minutes
> 		self.seconds = seconds
> 	
> 	def printTime(self):  # By convention, the first
> parameter of a method is called self.
> 		'''printTime:
> 			
> 		Prints the time.'''
> 		print str(self.hours) + ":" + str(self.minutes) +
> ":" + str(self.seconds)

Instead of writing a method that prints the Time, a more flexible 
approach is to write a method that returns a string representation of 
the Time. If you call the method __str__(), it is recognized by Python 
and used automatically by print statements. For example:

In [1]: class Test(object):
    ...:     def __init__(self, value):
    ...:         self.value = value
    ...:     def __str__(self):
    ...:         return 'Test(%s)' % self.value
    ...:
    ...:

In [2]: t1=Test(3)

In [3]: print t1
Test(3)

Writing a __str__() method gives the caller the flexibility to format 
the result further, such as printing two Tests on one line:


In [4]: t2 = Test(4)

In [5]: print t1, t2
Test(3) Test(4)

By the way, __str__ is an example of a "special method" - a method that 
is recognized by the Python runtime and used to implement bits of Python 
functionality. When you write
   print x

this becomes
   print str(x)

which is implemented as
   print x.__str__()

You can learn more about special methods here:
http://docs.python.org/ref/specialnames.html

Kent