Update python_oop.md (#356)

"instance data and functions" together are called attributes, not methods. I believe methods are just the function part.

Author: jaeyungkim

lectures/python_oop.md

@@ -192,7 +192,7 @@ In our example, an *instance* will be the name of  particular *person* whose *in
 
 In our example, two functions `earn` and `spend` can be applied to the current instance data.
 
-Taken together,  the instance data and functions  are called *methods*.
+Taken together,  the instance data and functions  are called *attributes*.
 
 These can be readily accessed in ways that we shall describe now.
 
@@ -894,4 +894,4 @@ class Polynomial:
 ```
 
 ```{solution-end}
-```
+```