Help with Classes

[Loismustdie129]

This may seem like a basic question but I still don't understand classes, I have tried all the tutorials. I tried to build my own class to return the python version and platform version, but it failed. If you guys could look at it and tell me what I am doing wrong, I think I can make better programs for python.

Here is the code:

>>>  import sys, os
>>>  class TestClass:
          "This class will return your python version and platform."
           def version():
              return sys.version
           def platform():
              return sys.platform

And here is the output:

>>>  TestClass.version
<unbound method TestClass.version>

[bartonc]

This may seem like a basic question but I still don't understand classes, I have tried all the tutorials. I tried to build my own class to return the python version and platform version, but it failed. If you guys could look at it and tell me what I am doing wrong, I think I can make better programs for python.

Here is the code:

>>>  import sys, os
>>>  class TestClass:
          "This class will return your python version and platform."
           def version():
              return sys.version
           def platform():
              return sys.platform

And here is the output:

>>>  TestClass.version
<unbound method TestClass.version>

You need to make an instance (live object in memory) of a class in order to use it. It also looks like you forgot the parens. that make a fuction call:

testMyClass = TestClass()
testMyClass.version()

[Loismustdie129]

You need to make an instance (live object in memory) of a class in order to use it. It also looks like you forgot the parens. that make a fuction call:

testMyClass = TestClass()
testMyClass.version()

I tried what you said, I tried to make an instance but it still didn't work. Maybe I don't know what an instance is but after I fixed it I got this output of testMyClass.ver sion:

<bound method TestClass.version of <__main__.TestClass instance at 0x00C5CFD0>>

[bartonc]

I tried what you said, I tried to make an instance but it still didn't work. Maybe I don't know what an instance is but after I fixed it I got this output of testMyClass.ver sion:

<bound method TestClass.version of <__main__.TestClass instance at 0x00C5CFD0>>

You're still not using "()" as in my example. But now you can see the difference between a bound and an unbound method. The latter comes from an uninstanciated class object. The syntax "testMyClass.ve rsion" merely asks the python shell to print the repr() of that object and would do nothing in a program. The parens are required to "call" the function (method): testMyClass.ver sion()

[Loismustdie129]

Thanks Barton, I am getting this now.

[bvdet]

This may seem like a basic question but I still don't understand classes, I have tried all the tutorials. I tried to build my own class to return the python version and platform version, but it failed. If you guys could look at it and tell me what I am doing wrong, I think I can make better programs for python.

Here is the code:

>>>  import sys, os
>>>  class TestClass:
          "This class will return your python version and platform."
           def version():
              return sys.version
           def platform():
              return sys.platform

And here is the output:

>>>  TestClass.version
<unbound method TestClass.version>

Define your class. The definition does not create an instance. Create an instance by calling a class object as a function (include arguments if required by the object). This creates an instance by calling method '__new__()' (this is transparent to the user), which, in turn, calls class method '__init__()' if defined. Instance attributes are then available and methods can be called. Methods will receive the argument 'self' automatically, so it must be present in the argument list. If you want the instance to be displayed a certain way by 'print', create special method '__repr__'. There are several other special methods - some are defined automatically and some you can define in your class. Example:

import sys, os
class TestClass(object):
    "This class will return your python version and platform."
    def __init__(self, s):
        self.data = list(s)
    def version(self):
      return sys.version
    def platform(self):
      return sys.platform
    def __repr__(self):
        return "You have created an instance of 'TestClass'"

a = TestClass('create a list')
print a
print a.data
print a.version()
print a.platform()

Interactive Pythonwin:

>>> You have created an instance of 'TestClass'
['c', 'r', 'e', 'a', 't', 'e', ' ', 'a', ' ', 'l', 'i', 's', 't']
2.3.5 (#62, Feb  8 2005, 16:23:02) [MSC v.1200 32 bit (Intel)]
win32
>>> dir(a)
['__class__', '__delattr__', '__dict__', '__doc__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', '__weakref__', 'data', 'platform', 'version']
>>> print a.__doc__
This class will return your python version and platform.
>>> print a.__class__
<class '__main__.TestClass'>
>>> for key in a.__dict__.keys():
... 	print 'instance.%s = %s' % (key, a.__dict__[key])
... 	
instance.data = ['c', 'r', 'e', 'a', 't', 'e', ' ', 'a', ' ', 'l', 'i', 's', 't']
>>>

HTH :)
BV

[bartonc]

Thanks Barton, I am getting this now.

You're welcome. Don't miss this thread.

[Loismustdie129]

Define your class. The definition does not create an instance. Create an instance by calling a class object as a function (include arguments if required by the object). This creates an instance by calling method '__new__()' (this is transparent to the user), which, in turn, calls class method '__init__()' if defined. Instance attributes are then available and methods can be called. Methods will receive the argument 'self' automatically, so it must be present in the argument list. If you want the instance to be displayed a certain way by 'print', create special method '__repr__'. There are several other special methods - some are defined automatically and some you can define in your class. Example:

import sys, os
class TestClass(object):
    "This class will return your python version and platform."
    def __init__(self, s):
        self.data = list(s)
    def version(self):
      return sys.version
    def platform(self):
      return sys.platform
    def __repr__(self):
        return "You have created an instance of 'TestClass'"

a = TestClass('create a list')
print a
print a.data
print a.version()
print a.platform()

Interactive Pythonwin:

>>> You have created an instance of 'TestClass'
['c', 'r', 'e', 'a', 't', 'e', ' ', 'a', ' ', 'l', 'i', 's', 't']
2.3.5 (#62, Feb  8 2005, 16:23:02) [MSC v.1200 32 bit (Intel)]
win32
>>> dir(a)
['__class__', '__delattr__', '__dict__', '__doc__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', '__weakref__', 'data', 'platform', 'version']
>>> print a.__doc__
This class will return your python version and platform.
>>> print a.__class__
<class '__main__.TestClass'>
>>> for key in a.__dict__.keys():
... 	print 'instance.%s = %s' % (key, a.__dict__[key])
... 	
instance.data = ['c', 'r', 'e', 'a', 't', 'e', ' ', 'a', ' ', 'l', 'i', 's', 't']
>>>

HTH :)
BV

Well thank you, that was the last part I needed, with the __init__ function. I just thought that I was doing something else wrong and I would change that later. But I guess I did that wrong too :-).