Class objects - Printable Version

Class objects - Printable Version

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Class objects - Python_User - Aug-25-2020

Hi all,

I can't place the following 'thing' in Python coding.

Why is the output of print (MyClass.f) in the code below, looks like this: <function MyClass.f at 0x01DDE190>?

class MyClass:
    i = 12345

    def f(self):
        return 'hello world'

print (MyClass.i)
print (MyClass.f)

Thanks.

RE: Class objects - ndc85430 - Aug-25-2020

Because f is a function. What did you expect? If you expected to see hello world, you actually need to call the function by putting parentheses on the end.

RE: Class objects - jefsummers - Aug-25-2020

Because you are not actually calling the function. Put a pair of parentheses after the f in the print statement and it will call it. You are getting exactly what you are asking for

Try

print(MyClass.f())

RE: Class objects - bowlofred - Aug-25-2020

That's the default representation of a function when printed (as opposed to when the function is executed). It's very similar for functions outside of a class as well. Are you expecting some other type of output?

>>> def myfunc():
...   return("Hello")
...
>>> print(myfunc)      # No parenthesis after the name.  We are referring to the object
<function myfunc at 0x105f07620>
>>> print(myfunc())    # Parenthesis after the name.  We are calling the object as a function
Hello

RE: Class objects - Python_User - Aug-26-2020

>>> def myfunc():
...   return("Hello")
...
>>> print(myfunc)      # No parenthesis after the name.  We are referring to the object
<function myfunc at 0x105f07620>
>>> print(myfunc())    # Parenthesis after the name.  We are calling the object as a function
Hello

The code above makes sense, I do understand it know. Knowing this information, I thought about the following class and having the same issue and doesn't get the clue.... See remarks in the code below as well.

class Game:
    def __init__ (self, title, year, price):
        self.title = title
        self.year = year
        self.price = price

g1 = Game("FIFA", 2008, "€50")

print (g1)              # why is this again refer to an object number?? I was expecting as output: 
                        # FIFA, 2008, €50 --> so all the arguments which are in the 'Game' class


print (g1.price)        # this line works properly and I do understand how the code is executed
print (g1.year)

Thanks

In addition to the last answer,

I try to 'follow' the code and visualize it, but I am getting stuck when the code reach the class Game

RE: Class objects - ndc85430 - Aug-26-2020

You need to override the special __str__ method to provide a string representation for the object.

RE: Class objects - snippsat - Aug-26-2020

As mention over __str__ and can also add __repr__.

class Game:
    def __init__ (self, title, year, price):
        self.title = title
        self.year = year
        self.price = price

    def __str__(self):
        return f'Title:{self.title} Year:{self.year} Price:{self.price}'

    def __repr__(self):
        return f'Game({self.title}, {self.year}, {self.price})'

Usage.

>>> g1 = Game("FIFA", 2008, "€50")
>>> 
>>> # Call __str__
>>> print(g1)
Title:FIFA Year:2008 Price:€50
>>> 
>>> # Call __repr__
>>> g1
Game(FIFA, 2008, €50)

__str__ should primarily be readable,and something you feel comfortable displaying to a user.
__repr__ are helpful for developers,here show how to recreate the original g1 object.

RE: Class objects - jefsummers - Aug-26-2020

Adding to ndc85430 - think about how you would expect the class to respond if you had a few functions in the class as well. __str__ allows you to customize the output when you print the class.

RE: Class objects - Python_User - Aug-26-2020

Thanks for the quick responses :)

But I am actually seeking for the reason of why this code is displaying the object number and not how I can show the print (g1) as FIFA, 2008, €50

RE: Class objects - buran - Aug-26-2020

(Aug-26-2020, 07:16 PM)Python_User Wrote: But I am actually seeking for the reason of why this code is displaying the object number

(Aug-25-2020, 07:40 PM)bowlofred Wrote: That's the default representation of a function when printed (as opposed to when the function is executed).

you didn't implement __repr__ or __str__ method, so that's what you get