1c. Instance Methods and Attributes

Question 1

What does an “instance” method/attribute mean?

Answer 1

It means a class method or attribute whose value may differ from instance to instance.

Question 2

Can you only create instance attributes/methods inside the __init__ function?

Answer 2

No. You can do it elswhere, too.

Question 3

How do you differentiate an attribute or a method that’s considered “internal” to a class and shouldn’t be accessed from the outside?

Answer 3

Internal methods/attribute names are prefixed with an underscore (_) by convention.

Question 4

Can methods/attributes that have an underscore (_) suffix be accessed from outside the function?

Answer 4

Yes. Underscore is only a convention that serves to tell developers that the attribute or the method is internal to the class. However, it doesn’t enforce this any further.

Question 5

How do you test whether an object has a certain attribute?

eg. object=book, attribute=_discount

Answer 5

By using the hasattr function like so:

hasattr(book, ‘_discount’)

This function will return True if the object has the given attribute, and False if not.

Question 6

What does an attribute or a method with a double underscore (__) do?

Answer 6

It gets the Python interpreter to change the value of the attribute, so that other classes will get an error if they try to access it.

Question 7

Is there a way to access a class attribute or method that has a double underscore (__) prefix?

Answer 7

Yes. Double underscore is not a perfect mechanism and there is a way around.

class=Book
object=book
attribute=__secret

solution=book._Book__secret