Hi fellow OCW student,

I have very fundamental questions about programming in general. I'd like to use a simple example as follows:
class Square(Shape):
def __init__(self, h):
"h: length of side of the square"
self.side = float(h)
=== here, why should I use self.side instead of using just side = float(h)? I kind of understand why, but not 100%.

Question

Hi fellow OCW student, 

I have very fundamental questions about programming in general. I'd like to use a simple example as follows: 
class Square(Shape):
    def __init__(self, h):
        "h: length of side of the square"
        self.side = float(h)
===>> here, why should I use self.side instead of using just side = float(h)? I kind of understand why, but not 100%.

anonymous · Answer

The `self.` part indicates that the variable is a member of the class and not a local variable. Suppose you try to write your code like this:

class Square(Shape):
  def __init__(self, h):
    side = float(h)

What is side? Is side a local variable, usable only inside the `__init__` function? Or is it a member of the class? To avoid this confusion, you'll need to specifically say that the variable is a class member by putting `self.` in front of the variable.


It also depends on the language (for example, in C++ you may, but are not required to, use `this->` to access member variables).